yes i run a lot of rigs with a single core processor. it doesn't matter if it's an intel or AMD.
and less is better. it's not a 'trend', it's good business sense. If i can save $5 on the processor, i can spend that on the GPU.
If you cannot get this and want to buy an extra core to fit into your voodoo, then feel free. however it's not supported by anything that you can demonstrate.
single core systems work fine with 4 or 5 cards.
next.
At this stage, I suspect you never used sgminer. Here is what happens CPU wise if intensity >20 gives the best performance:
Now, show us your sempron 145 running VNC/Teamviewer, cgwatcher and sgminer at maxed out hashrate/intensity/WU. Also show us your previous contribution in helping newbies at mining.