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I think you are combining multiple issues into one question, where the answer should actually be multifaceted.
A digital camera is made of the following parts: 1) lens 2) sensor 3) image processor 4) a casing 5) an interface (buttons, displays, etc)
All of those parts get an upgrade when making a DSLR, regardless of brand.
A better lens will dramatically increase the clarity of the images (known as Image Quality), can also let in more light (better aperture), and offer image stabilization (IS, VC, VR, etc).
A better sensor will capt the subtleties of your photo better, improve the range of lights that can be distinguished at the same time. Taking an interior photo of a window as an example, you can either expose for the inside, which is much darker, or for the outside, which is very bright. A professional DSLR will give you a better range, and you might be able to capture both. A good sensor will also influence how large you can blow up a picture (megapixels), and the amount of grain added by high ISO. A Canon S90 will have similar grain at ISO 200 as a T2i would have at around ISO 800, for example.
A better processor will let you take pictures faster, focus quicker and more accurately, and create better .jpeg images.
A better casing for the camera will provide better weatherproofing, and offer better impact resistance with sturdy metals instead of cheap plastics.
Finally, a better interface will let you tell the camera what you want to accomplish faster. Some point and shoots offer full manual controls, but will often hide ISO settings deep in menus, or make manual focusing insanely slow.
When you take all these into consideration, all things being equal elsewhere, the same photographer in front of the same subject using the same lighting will get better pictures with a DSLR than with a point and shoot. Can professionals such as Chase Jarvis take better pictures with a Lego camera than most people could with his Nikon D4? most probably. But give anyone a DSLR, and you will still notice an improvement in the quality of their photos.
As far as the crop factor affecting the aperture, I think Maestro doesn't understand how crop sensors function. Using a crop camera will not affect how much light the lens lets through. A 50mm f/1.8 will let in as much light on a T2i as it does on a 5dIII. If you want proof of it, take an external light meter, measure the light, and put the settings your light meter recommends into both cameras, and you will get more or less the same exposure (and if everyone used lenses measured in t-stops instead of f-stops, then you would get even more similar results). If a scene requires f/11, 1/400 and 400 ISO on a top full-frame camera, then those same settings will also work on a crop DSLR or a P&S.
But all that being said, most Point & Shoot cameras released recently perform much better than most top DSLRs performed 10 years ago. Even a lot of cell phones are providing very impressive image quality for something where taking photos is just an extra feature. The photos and videos coming out of an iPhone 4S and the newer droid cameras are good enough for many situations.
_________________ Cameras: Canon EOS Rebel T2i, Canon S90 Lenses: Tamron: SP70-300mm F/4-5.6 Di VC USD, Canon: EF-S 18-55mm f/3.5-5.6 IS Lens, 75-300mm f/4.0-5.6 III, and EF 50mm f/1.8 II Retired camera: Fujifilm Finepix s700
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