Well. its getting harder and harder to find PS/2 compatible stuff...
No.
Its dead easy. PS/2 compatible stuff is sold all day long every day continuously forever and ever on NewEgg and a zillion other places. Not only available but cheap too.
Just try and find a wireless mouse that operates on the 2.4ghz range vs the old less reliable 27mhz stuff... Logitech for example, made only one model of such mouse that i'm aware of.
I will be getting USB 
Wireless mice and keyboards sux. They weigh triple the weight (or more) of a wired mouse because of the big heavy battery. They cause tendonits, RSI, Carpal Tunnel Syndrome, RSD, CRPS, nerve damage and other horrible problems.
A mouse is something you put force into many millions of times per year. Due to the way hand anatomy is constructed, a mouse should weigh as little as possible and otherwise be user-friendly.
I have tried lots of wired and wireless mice and keyboards. I will be sticking with the wired versions which are cheaper, more ergonomical, cost less, are healthier, don't have to be recharged, have a lower price, and don't force you to downgrade to obsolete USB1.1
My PS/2 mice come with a 1M to 2M cable, which I plug into a 2M to 3M extension cable in the movie room. So the mouse and keyboard can reach anywhere.
I have 2 wireless PS3 joysticks which are only 1.5 years old and have undergone very light use and they are already having trouble keeping a charge. The other 2 PS3 joysticks are still 100% ok but I have trouble imagining them to still be working 5 years from now. The controllers were not cheap or anything. They were like $50.00 a piece. I am judgemental. When I pay $50.00 for a controller I expect it to last 10 years.
