Originally posted by Laurentiu Cristofor The Pentax advantage over Canon/Nikon is that they offer higher end APS bodies and lenses, and features like SR and WR. Canon/Nikon APS bodies have only recently become more competitive, but Pentax still has the advantage that their lens lineup is APS oriented.
This is either an advantage or a disadvantage, depending on how you look at it, but it is the big difference. Most every other manufacturer out there makes upper end lenses that are designed for 35mm sensor size and then expects the peons to mount them on their (upper end) crop sensor camera.
Nikon and Canon are big enough that they could (if they wanted) produce some nice crop sensor lenses. However, they don't feel threatened by Hoya and they make a lot more profit on full frame cameras.
It is a big difference though. If someone thinks that someday they want full frame, then they probably shouldn't start with Pentax. Sure, there is a 645D out there, but that is a pretty big jump up from the K5.