My interpretation:

Portal 2 was released after a clear move from Valve to develop for the consoles. They had released games on console prior to this, but were primarily a PC developer that ported games across to the console after launch. Portal 2 came after some very public announcemnts regarding (the complete turnaround of) Valve's attitude towards the PS3.

Valve take a lot of data to try and determine their customer's experiences through the game. In HL2 they used coloured overlays with maps to indicate hotspots where players died frequently, or got stuck.

I think that this has been misinterpreted by Valve, as a universally bad thing. Valve doesn't want you to get stuck, or repeatedly die, or stop progressing through their games. Since they now have a PS3 audience in mind when developing this game, the puzzles have to be fine tuned so that they can be solved by any system. This involves removing those solutions which rely on the twitch aiming possible by a keyboard and mouse player on CS:S or TF2 for example.

This can be legitimately calculated, I would imagine. Full rotation of 360 degrees on the PS3 with analogue stick on full lock = x. x is the absolute shortest time the movement can be completed in. If the time spent in the air is less than x, it physically can't be done on a PS3. Adjust this for skill level, and you basically rule out chambers that involve mid air portal replacements or on-the-fly ad-libbed execution. Their current audience, the PC audience, at least if I am an indication - like to be challenged. We like the areas where we died repeatedly, because we have a sense of pride over defeating them. I mourn the loss of difficulty.

They did pick up in other areas though, such as the script, plot and overall atmosphere. The game plays like an interactive Pixar film and is enchanting family fun in a way that video games for adults rarely are. While I am the biggest advocate of the more PC-centric style which they left behind, that of the original game, Portal 2 has far more mass appeal. Any game that introduces enough children to gaming that the reddit frontpage is literally flooded with drawings by 8 year olds has got to be a good thing.