I can't stress how much I value release notes, especially for closed source, commercial software. None of us want to invest on a piece of abandonware (unless it is ageless, which is quite unlikely for anything with a GUI), or a piece of software that is not completely abandoned, but takes a full year to adapt to the latest OS, campatibility-wise or UI-wise; and release notes, especially with dates, serve as almost the single metric for gauging developer commitment. In fact, whenever I try to learn about a piece of software that I heard about, one of the first things I do, usually after browsing through features and screenshots and before I even download the software to try out, is to look for its release notes and skim through it if available, and the outcome largely determines whether I'll even bother to download the installer.1 A prominent, dedicated page with dated, detailed release notes immediately leaves a good impression on me.
Unfortunately, many developers or publishers don't value release notes as much as I do. Several problems, in ascending order of seriousness:
Most release notes are not linked to from the home page or at least the download page, which kind of makes sense when the audience is generally non-technical, but there's little excuse when the software's targeted audience are pro-level or power users. This is not a big problem now because Google is very good at turning up release notes as long as they exist.
Quite some release notes are not dated, which I can't understand — it's so easy to date each entry, and it adds so much context, especially for gauging commitment (I guess developers who are less commited might not want to insert dates precisely for this reason).
For some software, releases notes are downright nonexistent, at least not on the web. Interestingly, occasionally they are available from an in-app menu or distributed document; the publishers just don't bother to put it on a web page. Not surprisingly, I might as well not bother to download this kind of software.2
If I were ever to publish closed source software, I'll definitely have dated, detailed release notes, linked to from the home page.
P.S. Speaking of release notes, it's hard not to complain about MAS, as if there are not enough complaints about this horrible platform. You can only view the most recent release with its release notes (and some publishers stack "bug fixes" notes of minor/patch releases on top of the real notes of the last major release, making it ever more confusing), whereas in the iOS App Store you have the "Version History" page that shows you a dated list of releases with release notes — what I would expect from everywhere. Basically, Apple has all this data and they can show it to you in a satisfactory way it they want to, but they blew it by not bothering to implement it. Note that I'm much more likely to care about the release notes of an OS X application than an iOS app, and I daresay most power users will agree with me.
Of course there are much more serious problems with MAS like the lack of trials, so the release notes problem is nothing but an insult over injury. In short, MAS is not a good distribution channel; it's only a lazy one, a compromise for small publishers.