Ok I really don't know what I'm missing, then, because unless I'm completely misunderstanding what you're after, IrfanView does what you want. From IrfanView I go to File >> Batch Convert/Rename and get a whole mess of options. By clicking the Advanced Options button on the right side, you get choices for a whole mess of nifty options, including resizing to specified dimensions, or by percentages..isn't that what you're talking about? Or am I confused?

Anyhoo...I'm sure you'll find a program that works for you...IrfanView works great for me because it's powerful, small, and completely free.