If you're asking specifically about late-model, auto-everything, bells-and-whistles SLRs, I agree that they're more similar to DSLRs than different---the main difference is in the recording medium rather than the user experience.

More generally, I think the answer is just that some outstanding cameras have been made in the 35mm SLR format; no wonder considering its popularity. I find myself shooting my AE-1 a lot simply because it's an elegant camera in use, not because it's an SLR per se.

-NT