I actually read that as a sign that Naxos is doing well. Prices seem to have drifted up over the years. I figure that the relative shortage of new classical releases from other labels gives Naxos some pricing power. The active labels I see most, e.g. Harmonia Mundi and Hyperion, have even higher prices for (truly) new releases.
[Disclosure: I'm not particularly a fan of Naxos, and buy their recordings only as a last resort, but give Mr. Heymann credit for developing a successful business model.]
On the other hand, I don't see how the Naxos catalog of "core repertoire" recordings could not be suffering as a result of the surfeit of cheap re-releases from EMI/DG/Decca/Philips/etc.