I work in an admissions office in a RG university.
It's just as happy says. We have lots of unknowns at this time of year and while we have a good idea of actual against target, we could really do with a crystal ball!
There are lots of variable factors: number of insurance offer holders who take up their place (or not), applicants who have met their firm choice offer but would prefer to go to their insurance choice anyway, applicants that wish defer, deferrals who wish to come now, applicants who withdraw entirely.... The list goes on!
Universities can also choose whether to be in clearing for home/eu or overseas, or both. While a university might be present on the clearing lists, there may only be a handful of places. We only had to find 4 students in clearing this year.
So, in short, the answer is no: if a university is in clearing, it doesn't mean it'll lower its grades next year. If anything, we need to at least maintain grades required as they reflect the calibre of the student, and this has a direct effect on our position in the dreaded league tables ....