For a megazoom and PS camera, having more MP is not improving image quality.
For a full frame D-SLR or medium format digital camera, it depends on what your need is. For sports and action photographer, one does not need a lot of megapixels, as can be seen in models like the Nikon D3, D3s, Canon 1D Mark IV. But for those who do studio work, art work, need large prints and detail oriented work, having more MP can improve quality, especially many of these end up in large prints. These can be seen in models like Nikon D3x, Canon 1Ds Mark III and Canon 5D Mark II. So how many MP depends on what you need. Many people who own a full frame or larger camera also own a high quality large format printer. So they can benefit from more MP. In this category of camera, having more MP does not affect image quality much.
I also need to correct your statement that Canon outfit the APS C size camera with 28-135mm lens is a mistake. I don't know how familiar you are with Canon lenses. But the EF 28-135mm f/3.5-5.6 IS USM lens is an EF lens, meaning that it is NOT specifically designed for APS-C size cameras. The EF 28-135mm lens can be used for full frame and film cameras. On the other hand, the EF-S line is specifically for the APS-C cameras. Canon does have the EF-S 18-200mm IS or 18-135mm IS lens for the APS-C size cameras.
Nikon also has the 24-120mm VR lens which is similar to the Canon 28-135mm lens, both of these can be used with full frame, film camera and the APS-C sized cameras. This focal range is not a mistake. Different people have different needs. Fanatics of wide angle will want a wider lens with 16-35mm or wider (35 mm equivalent, or the 10-22mm for the APS-C sized cameras). For those who like all-in-one lens, this may sound like a limitation. Most photographers have a collection of lenses, wide angle, general purpose, mid range tele, long tele, macro, etc. So having these different focal length options give us more options, an advantage to buy into Canon and Nikon, not a disadvantage. Both Canon and Nikon have a long history from the film eras, so Canon's 28-135mm and Nikon's 24-120mm lenses reflect that they are mindful of the needs of both their new and old customers. So be careful about your accusations, do some research first.