Well, given that over the course of seven regenerations he never once showed any significant degree of romantic interest or attraction to anyone, even his most nubile and scantily clad companions, I can see some validity to the assumption. And even the 8th Doctor's kiss with Grace in the TV movie was more of an exuberant, I-love-the-world-and-everybody-in-it kind of gesture than something romantic -- it came straight out of the blue and rather gave the impression that he'd have kissed anybody who happened to be standing in front of him at that moment.

The 9th Doctor, on the other hand, is an outrageous flirt, so anyone starting from that point is bound to be awfully confused when older fans keep insisting the Doctor's Not Into That Kind Of Thing.