I chose Pentax in 2004 when I bought the *ist DS. I chose it for the following reasons.
Size - Smaller than the rest
11 point AF - Way more than the rest
Cost - Relatively cheap
AA batteries - Different than the rest
SD cards - The rest used CF and I already had an SD card (remember, flash memory was very expensive for very little storage back then)
The grip - Unique. Still love it.
Viewfinder - Pentaprism, different than the rest. .95% magnification, bigger than the rest.
Kit lens - We all know how well made the DA lenses are compared to Canikon, esp. their old ones.
For these reasons, Pentax was a a no brainer for a poor college kid upgrading from a point and shoot.