Axeman, given the friendliness of the kittens, and the fact the white one was still very very white, I figure someone had just dropped them off and they hadn't been there for long, and you are correct the owners probably hadn't figured on the cost of neutering TWO kittens and the cost of vet bills etc.
it is sad ..it does happen..I remember seeing a feral main coon hunting birds and mice at Col.Sam Smith in the spring time, I haven't seen him in a while either. The six open cans of food surrounding the pet hamper tells me that those poor kittens did NOT eat them, there was a racoon snoozing in the tree above them, and lots of squirrels running around. Anyways, I just couldn't leave them there, that would be inhumane. I didn't realize how common this was and how often this happens.
A real eye opener for me.