I'm curious as to whether how widespread this is. More importantly, what are the chances that of a certain film being on DVD when it has never been released on any other home video format? Can we cite some examples and maybe possibly even compile a list?

California Split didn't make it to any home video formats before DVD, IIRC.

DJ

Abel Ferrara's Driller Killer

Driller Killer was released on VHS. If nothing else, Magnum put it out on VHS in 1979 or so.

DJ

The only one I can think of that may count is Song of the South, which was never released on VHS or laserdisc in the United States. It's not on DVD yet, but it is rumored to be next year.

Probably one of the most requested titles, coming out this summer on DVD, was NEVER released on VHS: THE HIGH AND THE MIGHTY.

Several of the British comedies in the Carry On... series that are included in the Anchor Bay box set were never previously out on home video in the United States.

Some of the titles from the Universal franchise collections (I'm thinking particularly of the Ma and Pa Kettle and Francis series) are new to home video.

The Car (1977) had never been released on LaserDisc, VHS, or any other home video format prior to 1999. At one point in the mid-to-late '90s, Roan Group was going to release The Car on LaserDisc complete with a commentary track by James Brolin and Director Elliot Silverstein, but it never happened. In July 1999 Anchor Bay released it on DVD with a very nice 16x9 2.35:1 transfer. I think a VHS might have been released at the same time, but I'm not sure about that. Regardless, it took 22 years after its theatrical premiere for The Car to make its appearance on home video.

The very cheesy Kansas City Bomber
I saw it in the early 90s on Cinemax, they used to show a movie on occasion that was not on home video

Actually the entire run of Ma & Pa was released to VHS (including the final 2 films which haven't been released to DVD. I believe some of the Francis ones were as well but I'm not sure if the entire series was.

As for the topic on hand, were the Dr. Christian films (available from Alpha) ever released on VHS? I don't recall ever seeing them.

Carbine Williams has never been out ever....fix it

And don't forget 'Island In The Sky', which is being released on the same day as THATM.

I don't think we can technically include this title in this discussion at all, since it was released on LD and VHS (although not in this country), and it has not officially made it to DVD yet. Pretty much the exact opposite of what the OP is wanting to know.