I don't fully agree saying 2k5 is better than 2k1 that is better than 2k. Personally I prefer to have the BD logic board separated from Main board
And is not always true that the most recent model is better than the oldest (that is true is it is always cheapest to produce for the manufacturer...).
Example : CECHCxx versus CECHGxx
The most important difference in that models is the RSX
In CECH-20xx is 65nm
In CECH-21xx and CECH-25xx is 45nm
Also, there are 4 main RAM chips (with 64mb each) in CECH-20xx, and only 2 (with 128mb each) in CECH-21xx and CECH-25xx
By doing this changes sony reduced the power consumption and temperatures, and as a consequence it allowed them to reduce the wattage of the power supply, from 221w to 197w
There are other changes such the LAN wifi/BT and other stuff i dont even remember right now, for an overview take a look at this tables where are listed the most important components for every PS3 model
http://www.psdevwiki.com/ps3/Talk:SKU_Models
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Years ago when sony started manufacturing the motherboards for CECH-25xx with the bluray controller integrated in the main motherboard i thought like you... i did not like the idea of having that controller chip soldered in the motherboard because i remember very well the times of the PS2 when a laser pickup problem used to "blow up" components of the motherboard, that sucks (shame on you sony we will never forget it) and i was scared of that
But now it looks like a good idea, because in all this time i have not seen anyone ever reporting that problem in a CECH-25xx or newer models, it seems that part of the circuit is robust
As a benefit... in this boards there is no need to make any "remarry" if you change the bluray drive... actually you can remove the bluray drive completly and the PS3 will keep working normally (you can boot apps/games and there is no problem when installing firmwares)
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Manufacturing quality of the Playstations (the whole familly) can be represented in a graphic by a curve with a belly
The electronics always improves making the board more efficient (and cheaper too) and reducing its size, and removing components that was not needed (such starship2 , usb hubs, intermediate voltage regulators, and other small components)
Also, most of the motherboards has "unpopulated" pads and duplicated tracks and rails because they are very conservative and produces lot of revisions, this things are constantly "cleaned up" to simplify the board, this is good when done well, (and they uses to do it well)
But what i said in this paragraph is only related with the motherboard... actually the motherboards of the superslims are better than the slims
The problems are the other components of the PS3, like the heatsink and fan, this is the biggest problem of the superslims, together with the excesive butchering made with the bluray and the ugly chasis, lol
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I never liked the first PS3 models with partiall or full PS2 backward compatibility, i think it was a bad idea to integrate the GS/EE of the PS2 because this converted them in barbaques and the efficience is very low, with a power supply of 400 watts
Look at the PS4, the first model uses a power supply of 220 watts or so iirc, this was a nice start point (and later they ruined the efficience with the PS4 PRO, lol), and look at the newest intel and AMD APUs with 65 watts or less and are 14nm iirc and soon AMD is going to make the jump to 7nm technology (for the PS5, heheh) this is going to reduce a lot the power consumption, finally we are going to have consoles that doesnt makes noise like a yet engine and robust enought to not need to care about temperatures
So the evolution of technology was clear, but with the first PS3 models they was taking a diferent route, the problem they had at that time is they did not have ready a PS2 emulator made 100% by software, but in newer PS3 models there is one and seems to be good (when provided with accurate game configs, something sony did not made)
= THIS ONE:
Im still there right now! 