Handheld reviews: what do they tell us?

[Bodhesatva]

First, I want everyone to examine the metacritic aggregates for PSP and DS games. The PSP list can be found here:

http://www.metacritic.com/games/psp/

While the DS list can be found here:

http://www.metacritic.com/games/ds/

You will notice almost immediately, I suspect, that there is a grand total of 5 games (4 for DS, 1 for PSP) that have achieved "Universal Acclaim" with a metacritic average over 90. Comparatively, the Wii already has 8 such games, the PS3 has 10, and the 360 has 18. Any one of these systems has more than the DS and PSP combined. This evidence is stark and inarguable, I think.

So what is the cause? I think there are two reasonable explanations: either the handheld systems simply have a dearth of well made games on them, or game reviews have a noticable bias against handheld games. In your opinion, what is the cause of the disparity in how these systems are reviewed?