Sure, and that's one of the problems with server-side key strengthening. You start off making a cracker do a thousand or million fold more work. They go and get

Sure, and that's one of the problems with server-side key strengthening. You start off making a cracker do a thousand or million fold more work. They go and get better technology, like a GPU or an ASIC. So then you have to go upgrade your own hardware, or skimp and make the user wait for 1, 10 or 30 seconds while they login and you strengthen their password. It's an arms race and not something a star-topology (single server serving potentially thousands of users) is going to scale well on. You want those cycles rendering your HTML or doing something valuable. Client-side password stretching and memoization simply makes more sense.