I think the $10,000 figure is for non-retirement investing.

You are incorrect. The $10,000 minimum is for EACH INDEX FUND, regardless of what type of account they are held in.

I have my Roth IRA at Vanguard, approximately $15,000. I have it in 6 funds because I want to diversify. I'm not that worried about the $10/year.

If each of those 6 funds is an index fund, and you have less than $10K in each, you are paying $60/year ($10 X 6) for the funds, not just $10. These fees are taken by Vanguard directly out of fund distributions, so they are not readily apparent--most folks don't check what $ amount they were supposed to receive in distributions vs: what they actually did receive! (IMHO this is slightly underhanded way to charge fees by Vanguard)

2old