What makes the Nikon D3100 an entry level model while the D300, D3, etc are so great? - 1

I'm looking at the cameras, and I can't figure out why a camera with less mega-pixels is lower end camera. The D3100 has 14.2, the D300 and the D3 have 12.3. I understand there are other things involved, but unfortunately I don't know what (Sorry, I'm more of a film person… ). Could someone explain why it is exactly that this is still an "entry-level" camera? I'm looking to get a good DSLR, but I don't want to pay an arm and a leg just for bells and whistles that I'm not sure I'll use.

Megapixels are not at all relevant. The D3 is full frame, total different ballgame. ISO performance comes into play as does build quality and ergonomics.

A D3 is about twice the size of a D3100. A D3 will live trough a tropical downpour and keep shooting (recently there was a go who dropped one from a motorcycle doing 50, that kept shooting)

D300s is somewhere in the middle. DX sensor but buttons for everything instead of menu options. Ability to use every lens nikon made since 1976, serious weather sealing (I've been soaked quite a few times but my D300 kept going).

So, from the D3100 you're paying for feastures, the D5100 brings you a fold-out screen. The D7000 has an autofocus motor in the body and decent bracketing options… It goes up.

In addition to the things that Jeroen mentioned in the answer above me, the D300 and D3 are built like tanks. They have a magnesium frame. They have very good weather seals. I mean, you can't use them underwater and I'd think twice about using them outdoors in a downpour, but I've shot several jobs in the rain with my D300 over the past few years and it's still going strong.

Another thing to consider is that the D300 and D3 (etc) have many more functions available directly through buttons on the body so you don't have to step into the menu system to make changes quickly. They are also bigger, which makes it easier for some (me included) to operate the controls. I've shot with my D300 while wearing gloves with full fingers. The controls are spaced out far enough that this is possible. On a smaller camera, the buttons are jammed right next to each other and this would probably not be possible.

They are just made for people who make their living with the cameras so they can get the job done as quickly and easily as possible, knowing that they can rely on their equipment to hold up and function under some difficult conditions.