Well, I've read that the average "life-span" of a species is about five to ten million years -- I don't know what the variance is, but I'm not particularly surprised that a 25 million year old species is known.
Most animal genomes consist of a large portion of non-coding "junk DNA" that would be free, more or less, to randomly mutate -- the so-called "molecular clock" -- I would expect that the
genetic distances between this amberfied ant and a current one would be similar to that of a human and a late Oligocene "monkey" (note my use of the fancy word "Oligocene" in a desperate attempt to regain credibility).
I admit that your example does appear, though, to weaken my actual point a bit.