The wear pattern you described on your tires is called Feathering and is caused by incorrect toe setting.if the alignment was not done correctly they are responsible for not only correcting the alignment but also replacing the two front tires, just my two cents worth I hope you get it all straightened out.
I looked up some pictures and yes, that is exactly it.
I totally agree. They need to replace the tires. It's going to be hell to get them to do it, I'd imagine. Any tips on how to approach that conversation? Do they really expect a layman to be able to notice the very beginning signs of feathering and to take it to the shop that did that work within a couple of thousand miles? I've got a pretty keen eye, and it's not severe yet by any means, but that's definitely what is happening to my tires.