Hmm I think there is a big difference between picking meat off a pizza and using a grill that is the same as a grill that cooks meat.
For me, a huge part (although, not the only part) of being vegetarian (and indeed vegan) is not creating a demand for products I consider unethical. For me, meat is unethical, and if I buy (or encourage the buying of, ie: by eating something someone else has bought) a product with meat in, I'm encouraging the production of meat by creating a demand. Whether I eat the meat or not, doesn't really make a difference, as far as consumerism goes. I've created a demand for pepperoni pizza, even if I didn't eat the pepperoni. Does that make sense?
But using the same grill as meat products doesn't create a demand. It's just cross-contamination. If I keep eating veggie burgers cooked with meat burgers, it doesn't result in an increased demand of meat burgers (but it does of veggie burgers! which is good). I understand why people don't want to eat them, but for me, that isn't really an ethical thing - it's a personal thing. Like, it just grosses some people out, or whatever.
So, in my mind, if I'm eating something where meat is an ingrediant, I'm creating a demand for meat. If I'm eating something that's been contaminated with meat products, I'm not. That's where I draw the ethical line. Sometimes I might not want to eat something cross contaminated for "ick" reasons - not usually, but if something was contaiminated to the point it tasted meaty I wouldn't want it.