They could be small insects or worms, actually. It happens a lot. Do a search on the web, there's a lot of people experiencing the same thing, and a lot of people who have opened up their panels to prove it.
Bugs like banana flies and pretty much every other small flying insect can easily get stuck inside the panel. So throw out that old garbage bag filled with small flies and open up the panel and use compressed air on it (or just turn it in to Apple). Same procedure if it's dust (it does looks like dust in your case). Panels that aren't tight (many screens really aren't tight enough) can easily get stuff between the actual panel, and the plastic/glass.
Usually, when it's just one or two small spots, it's just dust, but when it's multiple, it's probably insects. And they do look different from dead pixels or sub-pixels as well. If there's sort of an fluffy edge to the spots, and some of them seem to go along more than one pixel or sub-pixel, then it's not the pixel that is dead, but something blocking the light. In your case, it does look like dust though, but usually that amount of dust doesn't get in between the panel and the plastic/glass at the same time (unless there's some fault in the construction, or you've done something really weird to your laptop).
If it looks like dead pixels, then it might be some sort of panel error as well, probably from production, but usually when experiencing multiple dead pixels (5-10 or more), they tend to flock. If you know you've done something stupid with your LCD display, it's sure to have been that though, so don't be too quick to blame the manufacturers. Not that I think it's the pixels in your case.
on the back!