Defining "cruiser" is pretty hard to do, as the term is fairly ambiguous by nature, and they way ppl choose to "cruise" varies a lot along our collective timeline, as well as by geographic location and riding conditions. Upthread, Jhn Hood mentioned that coaster-only bikes wouldn't suit his terrain, as it's quite hilly. I thoroughly believe him. I live on the coastal plains, so coaster-only works fine for me, although I like to run a front brake, too, for panic stops and for the extremely unlikely event that my chain brakes....
(Although, true story, last week i finally killed my first Velosteel.... I already replaced the guts and it's perfect now, but had it failed under "panic" situations and I didn't have a second brake, that could've been disastrous. As it was, it was just mildly irritating.)
The point is, although the term "beach cruiser" horrifies me when it's misapplied, I'm willing to accept the highly generalized term "cruiser" for almost any bike that one uses for cruising. I've found that the Phila craigslist sellers have a newfound tendency to refer to almost any step-thru as a "cruiser", as well as various lightweights with upright bars..... and that bothers me, b/c it messes my searches up. I think sellers have a duty to be pretty concise in their ads, but i don't blink twice if someone refers to their Brit 3speed or a "ladies" step-thru as a cruiser. I don't even mind if someone puts a fat saddle and some swept-back bars on a retired mtb and calls it a "cruiser"....that's good enough for me, so long as they're cruisin' it.
Derailers on cruisers doesn't feel right to me, but it doesn't preclude the bike from being a cruiser. It just makes me uncomfortable. =D
As far as the 29er cruisers--- they are certainly cruisers.....what else could you possibly classify a Felt Burner or a SE Big Style as? They aren't everyone's cup of tea, but they definitely fit the "Cruiser" bill.....
FYI: There's sure to be a 29r Worksman INB in my future. It simply MUST happen.....Well, a Worksman or some other industrial bike. Been eyeing up my Trailmate for 29er duty, but I'd have to change the fork...