1. DSLR is a system that can be customized according the specific needs of the owner, is very different from a pocket camera that is all in.
2. The difference in lens technology, sensors, image processors and operating the buttons on each camera, which in turn distinguishing character results.
3. Almost all compact cameras use CCD sensor size 1/2.5" Sony products, while the DSLR has plenty of options other than CCD technology, such as:
- Canon-developed CMOS (and later also used by Nikon)
- NMOS used by Olympus
- Full-frame, used for high-end camera Pro
- APS-C, used in camera entry level and semi-pro
- 4/3, used by Olympus and Panasonic.
The availability of equipment and accessories can be an important consideration. Buying a DSLR is basically buying a system. Once you buy it, the system will 'lock' you always use supplies and accessories that are compatible with.
In this case, I think Canon and Nikon have the advantage because - as an old player who leads the market - is a lot of 3rd party accessories available on the market, for example:
- Lens: Sigma, Tamron, Tokina
- Flash: Nissin, Metz
- Battery grip: different types of brands.
- Sony can use the Carl-Zeiss and Minolta lens.
- Olympus has an advantage in dynamic range and color saturation in addition to innovative technologies.
- Pentax can use the many old lenses that have been proven sharpness & quality.
- Technology will continue to evolve. Today's sophisticated body, in a few years will be out of date.
- The lens has a longer lifespan than the body.
- Ability to operate a photographer, sensitivity of capturing moments and technical ability are more important than the pursuit of technological development.