Just some general observations:

I live in southern California and I have noticed some patterns in the way video games displays are located in major retail stores.

Walmart:

The PS family has the front display, showcasing the PS3.  A total of 4 shelves are dedicated to the PS family, all up front so those are the first games you see in the video game/electronics aisle.

Next is the MS display with 2 shelves of Xbox360 games.

Finally the Nintendo family display which is in the rear of the aisle and consists of 2 shelves as well one for wii and one for DS.

Target:

The PS family has the front display, showcasing the PS3.  One side of an aisle is dedicated to the PS family, all up front so those are the frst games displayed in the video game/electronics aisle.

Next is the MS display, one side of the aisle behind the PS family.

Finally the Nintendo family display which is next to the  MS aisle.

Best Buy:

Aisle location seems pretty neutral as no one brand stands out as the main one.  However, the game demo area consists of three large LCD screens (over 50") the two front one, thus the ones that first grab your attention are for Xbox and PS3 showing Rockband and GH:WT respectively.  The screen behind has Wii sports set up (apparently this particular store had it set up with a regular video cable and running 4:3).

These of course are merely observations in my area consisting in a total of 7 stores, thus anecdotal and not determinative of an actual pattern.  However it opens itself to some analysis.

For the sake of argument, retail stores showcase their star sellers, and given this site's sales numbers, the Nintendo aisle should be the dominant one in these general retail stores. But it does not seem that way. 

What other reasons could this be? maybe the PSX/PS2 era mentallity is still strong; or maybe these displays are influenced by the corporations themselves (thus Sony Corp. giving incentives to maintain certain priority)?

Or maybe the obvious answer is that despite the sales records here posted, Sony still creates more revenue for these retailers.

It would be great if someone could provide an analysis on which consoles generates the most revenue for the retailers instead of the manufactures.

any thoughts, opinions and critisisms?

I think Sony made some kind of deal to put its stuff in front at Target and Wal-Mart or something. Really, PS2 games in the front? Anyway, I don't think retailers are biased against Nintendo because:
1. DS sells. A lot.
2. Wii sells. A lot.

Selling a lot=money=good.

Yeah, Sony making some kind of deal is very logical. But in the case of the GH:WT demo dsiplay, why is it shown with the PS3? GH has become a Nintendo/MS stronghold; and while I have seen demos played in the Xbox, never have I seen any non-nintendo game demo at any store.

Most of the game shops near where I live do this too. The Wii and DS stuff is at the back with 360 as you walk in, and everything else is stuffed inbetween. I don't think there's any particular agenda, just that with Nintendo doing crap last gen, things moved that way and the habit stuck.

I just want to make clear that I am not against Sony in any way, and although I am a nintendo fan, I have great respect for the Ps brand and I think the PS3 is a great piece of hardware.

I've been to several GAMEs in the UK and the Wii seems to be getting more and more space. I guess Sony must have made deals with retailers in the US?

When it comes to Gamer Stores it makes sense to put PS3 and 360 in the fore front. These stores target the same demographic. While stores like Best Buy, Future Shop, Target, The Bay(whatever your country version is), are best suited to display the current market leader.

Is there some bias. yes there is. Last gen GC was as hardcore power wise as you could get. It needed more display front to sell. Same with Xbox. However the Gamer Store catered too PS2 and Xbox. PS2 was the market leader. So why is it still the same?

Indeed there is a bias. It has to do with the 2 generation control PS had. Many of gamers that work in these stores fully entered the video game era when Sony took the reigns. Now that Sont is on the way out these Gamers don't want that change. So they are activly keeping their prefered console in the front. When they can. In some cases it's still a marketing move.

or maybe everybody knows (they are not ignorant Wii sold 2 millions last month) that Wii and DS will sell EXTREMELY well, whatever may happen, and they decided to show other products which are less likely to sell

(who said PSP, PS3 or 360 ?)

Same here (Wii/DS at the back).

I think it is mostly inertia.

First retailer to put Wii/DS up front *and* to do proper recommendations based on gameplay rather than hype will make a killing.