On the netbook theme, it was originally Microsoft that used licensing to limit the amount of RAM they could ship with (1gb?) and support(2gb). This made it impractical to sell anything in the low end on screen size, etc, but above their limit on RAM. It was already impractical to sell anything but windows unless you sold no Windows or AMD if you sold any Intel.. So Microsoft/Intel licensing and illegal behaviors kept a gap in every vendors product line between terrible and medium range for as long as they could.
I think in the next phase, the factor was Intel, older Celerons support more RAM, but Intel realized cpu constraints were no longer as significant as memory constraints, so maxing out RAM on an economy system was outperforming their middle range.
The vendors themselves are IMO far too disorganized to be behind these factors, the death of the desktop/pc is largely about consumers avoiding the results of tactics organized by Intel and Microsoft to maximize their own slices that the vendors got no piece of. The only real exception is clutterware, but even that was probably tolerated and maybe encouraged by Microsoft. They had an interest in obfuscating sources of clean media aside from paying them directly at the time and it also let them claim vendors had sources of income to seek out and later to redirect blame.