I'm often amazed at the way the 'tech community' react to such things, a little bit of knowledge is a dangerous thing and all that.
First off, a camera isn't just about megapixels, everyone knows that, the main thing is it's a great simple way of marketing this fact to people who are a bit dumb.
If you really want to understand why people like me are excited by the 808 and the 1020, you need to understand digital imaging a bit better. Most important is the Bayer filter pattern.
A good question is why does my Pentax K-5 with its Sony made APS-C sensor, have 16.3 megapixels, but produce images with a resolution of 4928×3264? Well because whilst people say megapixels, they actually mean photocell sites.
Pixels are then extrapolated from that the data of almost always a bayer pattern. In effect that means a 'true' image can really only be generated that is 1/4th of the size of the sensor or better yet 1/16th.
Effectively, all 'standard' digital sensors are upscalling. This isn't good.
Yes, a sensor is just one part of the chain, but it has probably the biggest difference to make on a mobile phone. Making small lenses is really rather easy, as it is a classic production problem where the more you need of x to make y, the higher the risk of bad x creating a bad y. So going with Ziess who've been doing this for years is smart and likely to not make any massive issues (like the iPhone 5 had).
So to re-cap, they can offer a zoom, without taking up any space. A zoomed in image will look as good as any other smartphone image would unzoomed, that's not bad. But mostly the downscaling will create very sharp images, this is handy for landscapes or macro work or just getting the details such as human hair. Upgrading from the 808 by going for a BSI sensor, which is floating and active stabilised should allow for good quality low light and stable video (previous complaints of 808).
The proof as they say is in the pudding, ultimately we will see if the shots are that good, one thing is certain, its very likely to be the best camera phone on the market, by a wide margin.
Is calling it 41megapixels marketing blurb, yes, absolutely, my understanding is it never uses more than 38 of them at a time. But considering how most people don't even understand how their eyes work (and bias certain wavelengths etc) I can see why they don't bother trying to explain.