Having used quite a few "normal DVRs" I can easily respond, there remains significant differences when it comes to overall UX. The TiVo still enjoys important differences that relate to overall usability, reliability, and control.
Yah, it was fun watching that exact argument go south on them.
Since TE4 (and they've all switched to TE4 for various reasons) - the UX difference between the current X1 and the Tivo has shrunk more than a bit. Those who appreciated the UX of TE3, especially over a regular DVR - now kinda isn't thrilled with TE4, and figures screw it, they're all the same.
Reliability, well, they've all suffered a rash of Bolt hard disk failures. Now, they've never experienced a rash of Comcast DVR hard disk failures so they don't actually know that Comcast DVR's are usually worse, but they all have Bolt HD failures (which are no different than Unit Failures) fresh in their minds.
And further, the mention of reliability also unleashed a string of complaints of missed recordings (All guide data related), which spiked dramatically post Rovi conversion - complete with recent (and valid) complaints. All cases where their friends "Regular DVR"s had no problems recording their shows, but the fancy expensive Tivo blew it.
It's really, really has become a harder argument than it used to be.