I don't think it is unpopular at all. From what I understand and know it is very popular with corporate clients. Essentially the perfection of a line and form factor with bugs and limits of prior iterations all addressed.
That is very different than it being cutting edge and of interest to narrow groups such as here where people are interested in hacking, rom development and the cutting edge.
I don't know of anyone who is unhappy with theirs. If you know windows mobile and want a solid non-slider front qwerty this is perfect.
It is hardly "too little too late" from that persepctive.
Palms problem was its debacle with the 800w. The 800w was "too little too late at launch" and ahd so many problmes that it got discontinued faster than any phone. It had borken features Palm was never able to fix, very very poor battery.
My Sprint store was never able to sell the 800w, even at $100, but they sell Treo Pro very well.