I paid $600 for a custom blog skin back 2007. As part of the package, it said PSD included.
When I eventually tried to open the PSD - around two years later - It was just one layer - and not even full size! More like a screen capture saved as a psd file ! lol
Of course, the company is now no longer around...
I dont care really, but if I were to ever purchase another thing of that kinda value, yes, I would expect a PSD.
Not so much so I could could do 'DIY' changes - Just so if the designer disappeared, I would be able to get another designer to make the changes.