Those 30 nights could be more pricey than the 50; shrug.

I think a wise program sets it up to reward both, because people's travel patterns vary.

Similar to some of the airlines offering elite status based on either # of miles or # of segments. Some people do a lot of segments (btw - those are often more expensive than longer mileage trips), so might hit 1K (using UA as an example) doing 100 segments but not have hit 100,000 actual miles. Since UA offers both to qualify for elite, there's more incentive to stick w/ UA than to go w/ an airline that offers status based only on miles (or a hotel chain that offers status only on nights & the nights are significantly more than the rest of the hotel chains).

Cheers.