Right but even with the megapixels race, we've gotten better imaging processing chips and what not. So the 13MP you have might be junk pixels, but so was the 5MP camera back in 2009. You end up getting more junk pixels to give you a better overall image than fewer junk pixels.
So I'd argue that with higher resolution pictures, we're actually seeing some benefit in cropability. While I do agree there's a megapixel race going on, let's see if going back to 2005's 2MP cameras gives us better images. I doubt it. And while HTC's camera might give you decent low light exposure, in a lot of cases the 4MP just isn't sharp enough due to lack of resolution in broad daylight.
you're right on the math and technological improvement over time, but when i say not really, what i mean is that phones take crappy pictures suitable only for viewing at small sizes. 'digital zoom' is the opposite of viewing at small sizes because all digital zoom does is make the viewing size larger and then crop off the rest.
from a math standpoint, nearly 4 pixels + image processing should offer more detail than 1 pixel (assuming we're not at a point where electrons are randomly jumping around, though from klug's calculations we are there for red).
however, i'll take a 6 or 8 mp SLR pic over a 13 mp cell phone pic any day. that's due to sensor size being the 800 lb gorilla of image quality. similarly, i'd take a 150 mp SLR pic over a 13 mp cell phone pic any day (similar pixel densities).
frankly i think HTC has gone too far with the MP-myth myth. even though larger than others' sensors it's still a tiny sensor and HTC's previous f/2 leadership is nearly gone with the GS4's f/2.2 lens. between the sensor and the lens they've got maybe 1/2 of a stop advantage in exposure.