Perhaps Aveda is under the impression that requiring deposits will elevate their status to that of the "finer" salons, some of which probably do require deposits to hold an appointment.
I happen to believe that there are enough salons in this world, and enough good hairdressers (some of whom are stuck at "lowly" salons, their fabulousness yet to be discovered) that finding one that doesn't insult its customers in this way is simply a matter of asking around, or picking up the yellow pages.