I would assume the system does restrict resources. It would have to in a case like this of running more than one application at a time. Unlike a computer, the Vita does not have anything to fall back on should resource usage reach its limit. Take RAM for instance. When a computer is unable to hold all of its active (and inactive) programs in RAM, it relies on virtual memory for management. The Vita has no setup like that, and the only logical approach for this I can think of would be to do something like the 3DS does. Allocate enough RAM for just the OS and other background programs as one section, and games take the rest. How much for the OS? I don't know, but enough for its needs. If Skype doesn't take from the OS allocation, then it is taking from the game allocation, to which complications could arise. If it is taking from neither, then there is a separate allocation section of memory tied directly to such programs, not used by the OS or games, so limits are placed on each.
As far as the CPU is concerned, while technically it'll handle multi-tasking just fine, it'll have the same problem that computers do when the load is too much. Slowdown. I would assume they went with their PS3 approach, and have one SPE (or in the Vita's case, a core) specifically for the OS and such programs like Skype so that they won't interfere with the games.
Restrictions of resources.
Obviously the area of memory used by the system
is not accessible via User Mode, but that doesn't
necessarily mean that the amount of memory dedicated for background applications has to be
*fixed*, the OS may simply
request allocation of memory and said amount of space in RAM will be allocated for it, similarily to how the PS3 handles it - memory allocation between levels can fluctuate. As for the amount of calculations background processes require, this also does not have to be fixed or dedicated to any specific core.
We don't really know how the OS of the Vita works as of today but my guess is similar to yours - that they went for the easy way of handling things and dedicated a single core for the OS simply because the Vita does
*a lot of stuff* in the background as it is.
The way I see it, one core is dedicated for the OS, no matter how intensively it is used, RAM is allocated dynamically and the remaining three cores work in a Performance on Demand scheme to prevent draining the battery even quicker than it already drains. Sounds about right?