Where To Get A Nikon 100mm F2.8 Repair Yet Another DSLR Question...?

Yet another DSLR question...? - where to get a nikon 100mm f2.8 repair

Although I probably asked a dozen questions DSLR recently, I'm a very analytical person who wants to have the good things ... and my friend had a Sony A300 today, and I either a Nikon D5000, T1i Canon, Pentax K20D, or ... but I was looking at the back of digital SLR since my first (even tho I know a lot about how to use digital SLR) ... I have given the A300 ... But my biggest question ... Why are Nikon and Canon so hailed? Have compared Is there really an advantage for one of them, Sony and Pentax? I refer to the specifications seem to be so close, and some cameras are better in this area, and another ... just want to know why it's so much hype from Nikon and Canon ... What they offer is better than another? The prices are ridiculous compared toSony and Sony also offers what appears to be a body and lens better ... then ... Why is this so? Is this a situation where they are more or less pay more than the name of the product? I expected a Sony A300 with a macro lens 100mm f / 2.8 to find is ... D5000 compared to a target 105 mm f/2.8 with ... D90 or just because thats my favorite because of their body weight and in particular the size ... Why are they so expensive? Is it worth the money ... And not just say "Yes", please explain your thoughts ...

thank you again