(it's "quoted" because it feels less like I'm diverting the thread topic this way! if you want to know about Vegetarian Weightlifter's diet; read on / ignore

)
Egg and Milk are very different to the stomach lining of a cow or gelatine. You can get eggs and milk without killing or harming an animal, hence most veggies eat milk and eggs. But a lot of veggies won't eat gelatine or whey.
There are of course moral issues such as "but eggs could turn in to a chicken if you let it" and "a cow needs a child before it gives milk, what happens to its calf?" etc., but that's each to their own opinion. I choose to be ignorant about the fact a calf was born - as far as I'm concerned, I'm still not eating a dead cow. As far as eggs go, two things; I'm pro-abortion. It's as much of a chicken as a human cell is a person. Secondly, presuming the egg isn't fertilised, it would never have been a chicken anyway.
I think a vegan won't eat anything that isn't a plant or plant produce. But a vegetarian will. Some "vegetarians"
do eat gelatine, whey from cows, etc., but really there's no sense in it. I know a cow isn't primarily killed for its whey, but the fact is it is from a dead cow - a cow had to be killed for it. Unlike milk.
So yeah, I won't debate or anything unless it's in another thread 'cos this could be a good thread if it's kept on-topic

But there you go! That's why eggs and milk are different to whey and gelatine (in my opinion, anyway).