Why do they say, they are patches and not full blown firmware. The way I see it, as non-coder do is that the 1.50 upgrade is about 13mb and 2.0 upgrade is about 16mb. Speacking from the past experience, most full blown firmware are generally have fixed size(but not neccessary always). Although the actual data that held insize are difference(revealed by pbp unpacker) but that could be because of the compression also. And I could be wrong on that note also. I doubt that the actual firmware need to be on the PSP internal memory first before the actual upgrade procedure begins, and therefore if the data that hold inside is a full blown firmware, it could still be compressed in the pbp. Also, theoraticlly if it is in fact a groups of patches, then it's weird that the actual files size of the 2.0 upgrade is not as I expected. Let me explain. on 1.5 upgrader, the manufacturor only have 1.0 firmware to deal with, therefore the patches could work, although unlikely as that's not how normal firmware flash work(i could be wrong on that). But the 2.0 updater are difference, if the updater need to be able to patch 4 versions of PSP(1.0/1.5/1.51/1.52), it should be much larger than just 3MB extra.
If who ever solely believe that it's just bunch of patches, then please give me some technical info here. I very would like to know. Seriously, although I'm no coder. But I used to do little programing in many languages. I did some PC mods, networking(went to 4 cisco classes in addition also) And I use both Windows and Gentoo. So, I'm somewhat savvy enough to know what you talking about(and if I don't I can always do more research). So, please do explain.