if u refer to nokia 808, they resample their photos from high megapixel to low megapixel
to deliver sharp, detail, clear, high colour depth & increased dynamic range photos
where a 4mp photos cannot totally outwin them in sharpness & detail
which u can do it on ur photo too, by using photoshop n choose the best resizing method
or by just simply upload to website like flickr or facebook n let them do the job,
thus noise on the photos will get reduces, & this method is being used by many high ISO cameras

larger pixel unit size does capture more light, but does not mean
smaller unit pixel unit size capture less light, if u see lumia 920 & nokia 808 cases
nokia 808 uses larger sensor size thus pack more pixel thus capturing more light
even in sony basic camera tat uses exmor r outperform most of the basic camera
but y camera phone that uses exmor r cannot do that? tis is also bcauz of their sensor size

sony exmor r sensor uses 1.75 vs 1.4 in lumia 920, but why S3, iphone 4s,iphone 5 or even xperia Ars
cannot beat lumia 920 in night photo? this is because of the lens aperture f/2.0
allowing more light thus the sensor get more light, but lowering f/2.0 will make camera harder to focus
which is why u see review saying lumia 920 produce soft daylight photos, but improved in new updates

there r many more ways to capture more light, like using BSI instead of FSI
or make mirror in sensor module more efficient to direct light on the sensor
or instead of RGB sensor, they use RGBY/RGBG/RGBW... etc sensor
or stacking sensor together, or making small pixel sensor so tat they
can be packed more compact to each other n many more

thus tis is y u see, when canon or sony release new sensor,
they did not brag about the pixel unit size nor the megapixel
instead they brag about how many light that their sensor is able to capture
but people mislead when they saw the increasing of megapixel trend, which is not the camera maker's fault