I guess I am one of those Catholics who left the forums for a while because it is hard to walk around in real life all day thinking "People are seriously that unwilling to enter into civil dialogue?" Obviously, the people in question are a tiny tiny minority on the forums here, but it's usually the little things in live that drag us down, eh? Anywho, here's my two cents:
1) Communion and why non-Catholics are not to partake in Catholic Communion: Apart from the other reasons mentioned above, communion is also what is says in the name...Communion! All Catholics are supposed to be in communion with the teachings of the Church, ie believing all things that the Church teaches as truth to be true. If you believe that the Catholic Church holds and teaches all truth necessary for salvation, then chances are you are either already a Catholic or are well on your way to becoming one. If you are Catholic, you are in communion with the Catholic Church and if you are converting to Catholicism then you will be in communion with the Catholic Church soon, and once you are, you may receive communion. If you are not Catholic, then you are not in communion...so why would you say "I am in communion with the Catholic Church" by the action of receiving Eucharistic communion while not actually being in communion with the Church? The Eucharist, apart from what we have said above, is also a way in which Catholics express and continue to be in communion with other Catholics who believe what the Church teaches, so it would not make sense for non-Catholics to receive communion. This is why Catholics don't receive communion at other churches when we visit them for weddings/funerals/baptisms. We also don't partake in communion with the Orthodox, even though we believe that their Eucharist is every bit as valid as ours, because doctrinally and historically, we are indeed not in communion.
2) As for the Ten Commandments: The original scriptural text never placed the commandments in a 1-10 order nice and neat like we are used to today. They were all simply listed. How we list the commandments as statements starting from 1 and ending with 10 is simply a matter of tradition. Catholics have traditionally numbered them the way we do, the Orthodox have traditionally numbered them the way they do, and protestants/non-denominationalists have likewise traditionally numbered them they way they choose to (though it would seem most of these Christians have chosen to follow the tradition of the Eastern Orthodox Churches). No matter how you number them, the scriptures say the same thing in all of our respective Bibles, and we all can go right to it and look them up.
3) Bowing to statues: I personally have never witnessed this, but my personal experience does not mean much in the grand scheme of things. I reckon it happens. On second thought, I have no doubt that it happens. My mom thinks that before taking a test, she has to kiss a picture of me or she will fail. Obviously, how well she learned will determine if she will pass or fail the test, but she likes to remember that she is taking the test because she loves me and wanted to succeed so that she can move up in life and make me proud I guess, and since she can't kiss me directly, she kisses my picture. It is a symbol of her love for me. Her love exists without that symbol, but it helps her to see my picture anyhow.
This is how Catholics are with statues/icons. We know the statue/icon isn't what it depicts, but it is a reminder to us of the love that the saints had for Our Lord which led them to lead lives that have made us label them as Saints (saint means "holy" as we believe they are in heaven, and only holy things are in heaven). We honor their memory, lives, and the love that they had by showing some gesture, but ultimately, any good Catholic knows that such people were only able to live as they did by the Grace of God, and all honor and glory belongs to Him. The Saints serve to remind us of God's awesome ability to take something so fragile and imperfect (ordinary people) and do extraordinary things through them for the glory of his own name. God forbid anyone should actually dare to worship any of these Saints or the images by which they are depicted. Does it happen? Probably. Should it? Absolutely not. Does the Church encourage Catholics to worship them? Never.
4) Public Opinion Polls: The deacon at mass this morning preached on the Eucharist and said a recent poll reported that only 51% of Catholics in the United States believed that Jesus was present body, blood, soul and divinity in the Eucharist. It should be 100%, but it isn't. The poll proves that 49% of Catholics have either been sorely misinformed through bad Catechesis/Sunday School, or they are so arrogant as to believe they can pick and choose what the Church means to them (Cafeteria Catholics) and still consider themselves to be Catholics in communion with the Catholic Church. The thing about polls is that they tell us what people think, but thats it. Thankfully, the Catholic Church is not a democracy, and I hope no one's church is a democracy, because such a church would be like one built on sand, and public opinion would be the flood.
pax et bonum