Aging traditional meads in the upper 70s doesn't seem to be much of a problem, at least in the relatively short term. Most of my stuff is stored at 75F, and at a couple of years, seems to be okay. I suspect that for long aging (decades) proper temperature control is probably important to keep browning and oxidation at bay. Melomels with fruit don't do as well in many cases, and I've had several develop signs of oxidation. I've taken to using higher doses of sulfite to try and prevent this, but the jury is still out on it.
Fermenting at higher temps in an entirely different matter. The temperature tolerance of yeast listed on the package is their survival range, but it does not mean the results of the fermentation across that range of temperature will be equal. In most traditional meads, the results will be better tasting and drinkable sooner if you keep the yeast at the lower end of that range.
In high temperature settings, most yeast will produce increased amounts of fusel alcohols creating unpleasant aromas and the "hot" burning character of paint thinner that will take ages to mellow (if they ever do - I've been waiting 3 years for some). They will produce aromas of sulfur, and/or strong phenolic odors that smell like Band-Aids, medicinal odors, or burnt plastic. There are very few yeast that can produce a decent result at 80F. The only ones I would recommend (based on limited study) are K1V and D21. There may be others that will be okay, but I haven't seen them yet. Some yeast are particularly bad in high temps - Montrachet for example.
So while your yeast are bubbling along without problem, there's a good chance at that temp that they are making paint thinner that you will either toss or have to age for 2+ years.
There are a lot of ways to keep the temp down - a spare fridge, a swamp cooler using evaporative cooling, sitting in a water bath, etc. If you aren't using K1V or D21, you need to think about managing this. Even if you are using those yeast, plan on waiting a full year before the Band-Aid smell clears.
"Our results are merely the result of carefully managing the transformation of bee spit into yeast excrement."