Everyone here is very enthusiastic about Pentax so you're going to get some, well, enthusiastic answers. But I don't want you to end up disappointed in the long run, so read on.
The true answer is that yes, Pentax (like Sony and Olympus, the other "tier two" camera makers) doesn't currently offer the vast scope of options presented by the market-dominators Canon and Nikon. There's fewer lens options (both on-brand and third-party), fewer flash options, fewer accessories, etc., etc. If you want something special purpose, you may be out of luck.
I have a Pentax catalog that came with my grandmother's K1000, a film camera she purchased in the early 1980s or late 1970s. It's kind of disappointing to look at all the options they offered back then compared to now.
But, there's three important items of good news.
First, all of those lenses from that old catalog still work with modern cameras. That's pretty cool. (Canon, not so much. Nikon to a lesser degree, as I understand it.)
Second, Pentax as a company really seems to be "waking up" and moving in a good direction again, as the phenomenal K10D attests and what we've seen so far in the K20D confirms. I think the future is good.
And finally, Pentax offers a very compelling value proposition for the areas that it does cover well — and, they
do offer a reasonably diverse "ecosystem" with all of the bases covered to some degree and some real strengths in some areas. Pentax's prime lenses are very highly regarded and can cost significantly less than equivalents from other makers.
So, as someone else said, what you really need to do is look at what
you want to do, and see how well Pentax fits your needs.