The 30-day active user number DO include alts but do not count additional logins from the same account. So if you logged in 100 times or 10000 times, you would still be counted as one active user.
There's nothing much you can do about alts. Even if two users log in from the same IP address, on the same computer, it could be one person with two accounts, or two people who share a computer.
Maybe someone can do a survey, asking people how many alts they have, how many grids they're on, and how big those grids are. See if there's any correlation. I'd guess -- with no evidence either way -- that the larger the grid, the more likely people are to use alts because there's more stuff to do with them.
Of course, if a grid ranks traffic to individual regions, then region owners might use alts to beef up their traffic numbers. The InWorldz folks tell me that they don't do that, so there's no incentive to inflate the stats that way.