Why I buy Nikon over other camera makes

1. Nikon is one of the only camera manufacturers to have retained a common lens mounting system throughout all these years, the venerable F-Mount (ever since 1959 with the Nikon F. For more info click http://en.wikipedia.org/wiki/F-mount). I would stick to Nikon for this reason alone. This means I can use lenses dating back to the 1980s such as the E-series 75-150mm f3.5 on my 3-year old D70 (yes, of course you will lose metering but who cares with the ability to preview shots instantaneously). Which makes a huge difference in preserving the longevity of your system.
2. Nikon is one of the only camera manufacturers that still innovates and produces great film SLRs such as the F6. The legacy of photography is film. All photographers should remember this.
3. Nikon is the one of the only camera manufacturers who still persists in innovating with their products. As an example, check out the Nikon SU-800 and SB-R200 Macro Flash system (available as a set as the R1C1 http://www.nikonusa.com/template.php?cat=1&grp=4&productNr=4803) which replaced the slightly clunky Sb-29s.