I wouldn't say that all anime characters have big breasts. It depends on the genre and the type of series. HSotD.... obviously aimed towards men. Naruto, it's mostly the older ladies ( +hinata) that have huge boobs. Bleach, in here, it's either huge boobs, or flat. Not really any inbetween.
In most series that I watch it's about 1 in every..... 5 girls that have big boobs. And really, look around. That's pretty much realistic. Or even less so. I have a group of 4 friends. two or which have e cups or higher. Then the other two have b or lower.......
It's mostly the situations that they're put in that are unrealistic. aka, I don't know what series this is from, but I saw a clip of some huge breasted woman pulling a bazooka out of her cleavage.....
Or running around on rooftops with them bouncing every which way because obviously the chick who needs the most support doesn't wear a bra.
But then there are series that you cheer at because they had an opportunity to make it more cheesecake than it already is but they didn't *cough*birdy 2 *cough*
Yes big boobs are nice, but in moderation biggrin
Consider the poor characters well being.... and back.