A few things:
RJ11 only takes one line.
RJ14 takes two lines and will fit in an RJ11 jack.
RJ25 can take 3 lines, it also will fit in an RJ11 jack usually.
It's quote common (has been for some time) for PBXes to use RJ14. The fancy phones need power on the other lines to run their displays and lights. A lot of PBXes now just use powered ethernet jacks and thus use RJ45.
I think everyone refrences RJ11 only because its popular. I dont think I've seen an actual RJ11 in a long time... Just RJ14's with only one line in them. I know
I haven't seen an RJ25 is >10 years.
Many PBXs are made to work on standard phone lines, but most commercial and even some residential guys are just opting to use all RJ45 jacks so they do not have to stock/carry both. Also many home phone blocks are starting to use RJ45 for the jumpers so they can be dual use (like the structured boxes from leviton, etc.)
Ive been spending some time in So. Cal, living in track-homes built in the 2003 era.
the 4 homes I've been in (seperate gated areas) within a specific community (which is a few miles large) all have jacks with 4 outputs. 2 RJ45 outputs, and 2 Coax outputs. One of the Coax outputs is labelled CBL, another is labelled DSS. One of the RJ45 ouputs has a picture of a computer, and the other has a picture of a telephone.
They're still wired from inside to outside, just as they always have been, so you can plug a single line cable with an RJ11 into it, or go all the way up.
(not disagreeing with you here, re-affirming what you've said)