Ahh, I was reading it as one month's rent is uniformly apportioned over the days in that month. Of course, that does make things vary from month to month, but the sum of the days' rent does equal the month's rent. I suppose you could divide one year's rent over 365 days to get the true uniform daily rate.
I guess I was confused since they very carefully used 30 days instead of "one month" at places, but didn't both in this case.