I swear you have said the same thing before toastboy... or if not have at least been in one of the dozens of threads this has been explained.
The region: "Others" is missing a lot of data, and the older the system, and also the lower number of big sellers a system has, the higher the percentage of titles is missing data for the Others region.
The PSP is one of the oldest systems... which means some old games that may be still selling (albeit slowly, but together they will add up) will not be tracked... more importantly for weekly sales, and particularly for the PSP, is that ioi doesn't accuratly track much more than the top 100 weekly for the region, and because the PSP doesn't really sell software well, a big chunk of it's software is missing each week.
Give me a minute and I shal dig up a post I made estimating what the multipliers are for each system (I believe for total (not weekly) PSP software I have it being multiplied by 6-7 to get a rough estimate... while weekly figures are more like 3-4 times)
