It's actualy based on the zoom level of the timeline (which is retarded if you ask me - it should be configurable or something, so you can always make it 1 frame if you want).
Yeah, but with alt+arrow you don't have to take zoom ratio into consideration anymore. You zoom your timeline as you wish and move 1 frame with alt+arrow.
This is one of the things I hate about vegas. I want the left/right arrows to move 1 frame no matter how far in or out I am. But maybe it is just me who feels that way.
You could always use a program like "Quickeys" (I'm sure there are many others) that could define that pressing the right arrow really means you are pressing alt-right arrow.