It's certainly been a pattern for a while. Rare (obviously long since part of MGS) were/are based near Twycross, and Sierra Online were based in MFN long before it was cool.

Many years ago I once had to visit Rare for work and was surprised by the security. I wonder if part of it is that they aren't going to be visited by a constant stream of fans if they're harder to reach/find. From outside the gates it was totally un-obvious that it was the HQ of one of the most influential game dev studios of the 80s and 90s.

That being said, plenty of companies are still based in reasonably sized towns: Jagex and Frontier are both in a science park on the edge of Cambridge, EA in Guildford certainly used to be and maybe still are in an otherwise normal business park.