How come some religions have dietary restrictions, while other (apparently) don't?

Most of the major ones do: hindu, islam, judaism, buddhism, and christianity all restrict foods.

Hello Cogito....please explain why Buddhism 'has dietary restrictions'....I'm a Buddhist and not aware of restrictions!!!

http://en.wikipedia.org/wiki/Buddhist_cuisine
I don't know much about it.
DOn't think Confucians have many restrictions.

Christians were the main ones I was thinking of that don't have DRs. What can't they eat or drink?

Well, I was thinking of the "no meat on Fridays" and the lent 40 days. There are probably fringe sects with others.
I don't think i can make the pi55up, Write_On; I'm backing off the tree, (TT4 makes it less difficult to stick to that one!) and I have my boys that weekend.

Buddhists should be vegetarians going by the ethics and principle of the religion....(and I know the dalai lama isnt)...Compassion remember!!

Yes, yes, it's an individual thing. Certainly Tibetans can't be vegetarian simply because there are not enough vegetables to feed everyone in the mountainous regions of Tibet (and Nepal)...
In South East Asia in the early morning monks go on an almsround with their bowl (one of their few possessions, others being their own set of clothes) and people gain merit by filling the bowls with food (if they are lucky). The monks have to eat whatever is put into the bowl. It might even be meat but I guess this is a rare event as most people can't afford meat on a daily basis.
As for those of us in the west, well it's a personal choice...I rarely eat meat now....
You are right, Brock Lee, it's best to be compassionate and not go around encouraging the slaughter of little lambs (other post on this page)!