The N900 not only has additional 768 Megabytes of swap, but it is stored in a dedicated, fast NAND memory.
The best explanation yet, imho...
It is still unclear whether the N900 has an FM radio or not. Official specs do not mention it and there's currently no trace of it on the device, but remembering how it looked the same (and that even several months after the device started shipping) in case of the N800 Tablet until software enabling it was suddenly and unexpectedly released by Nokia, it doesn't have to mean anything. So we'll have to wait and see.
Regarding the small storage capacity for software installation, I am well aware of the /opt (actually, home/opt) directory providing some 2 GB worth additional space. But the problem is that it is NOT being used by installable software packages. The only software that installed there was Dataviz' Documents-To-Go whereas (if I recall correctly) the "guideline" is that all apps larger than 500 kB (including all dependencies) should go there. Apparently, this is being ignored. Even the "official" Bounce Evolution (17.5 MB) installed under root ("/") and ate a lot of that precious space.