Anybody have an idea what would cost an equivalent software for Windows? (Offering similar usability, high quality templates/samples/tutorials etc. Actually it wouldn't surprise me if no such a thing exists for Windows.)

I don't think you have to do that, it's far too subjective and there are free equivalents for a lot of stuff (Picassa for iPhoto for instance).

The easiest thing would be to knock the retail price of iLife off ($49) as that's where Apple seem to value it.

I don't think retail price really reflects iLife's value, if you need such a software. Because iLife only runs on Macs (sold by Apple), the price of iLife can be subsidized. Still, I agree with you that the value of any software (for an individual) is highly subjective.

Also, the big value of iLife comes from the fact that it comes pre-installed on Macs and integrates well with the rest of the system. That's exactly what Apple sells: a hassle-free experience out of the box. No 3rd party alternatives can offer that.