You raise a good point, and technically with a properly set up dev environment, you would't need to know all of the stuff I mentioned, however, when you're doing something as complex as coding, it's good to be really familiar with the platform (my belief is that if you're doing a non-trivial task, you should learn about it at the deepest level that is practical for you, both because you'll be generally better off, and because it will save lots of time when something goes wrong. The Open Source culture encourages that.). Also, my impression was that the OP didn't want to just scratch the surface and try to get by.
I think part of the problem is the power and scope of the Maemo platform; it's real Linux on a phone, not an OS designed specifically for mobile devices. You have to understand the paradigms it uses in a lot of depth, and if you're going to learn a Linux distro anyway (Maemo), then I would imagine the SDK developers figure that you can learn Ubuntu (which is similar). I see what you mean about it being a barrier to entry in some cases, but I don't see any easy way around it. More on this later...

This has been said many times, but keep in mind that the Maemo SDK is just one very small taste of what Linux can be, and also that it's intended for technical use. If you don't like Ubuntu, check out Kubuntu, or one of the other variants. The sheer magnitude of choice (even out-of-the-box choice) is arguably Linux's best strength and worst weakness, but if you like choice, then IMO you can't do any better. Look around a bit more - this website has archived screenshots of several different distributions, to give you a better taste of what's out there.
As was mentioned, Python + Qt should work on anywhere both of those are supported, however, the Qt build that's distributed for Mac is not the same as the Maemo build, so you'll probably want to test on-device or in the SDK. Technically, you could code in C/C++ on a different OS (if your IDE needs the headers to parse, you could just copy them from the VM), but you'll have to compile and debug in the SDK anyway.
I think you have a point, but not one that's easy to address. One thing I notice is that the SDK assumes a higher level of competency with Linux than is maybe strictly necessary. I don't know what could be done to simplify that without changes to the SDK infrastructure itself, but in theory the workflow could probably be made simpler for non-*nix users.