HGiles: And I honestly don't trust GOG coders with a client. Clients are *hard*. GOGs coders are obviously too incompetent/overworked to get their website working.
HiPhish: Web development is an utter mess of standards, exceptions, quasi-standards and standards that haven't yet been fully worked out on but everyone has already started using them. Developing an application is much cleaner by comparison. The worst you'll have to do is have several different APIs (like Windows and Unix) which you need to write a common wrapper API for.
EDIT: a great example is the
Transmission BitTorrent client, it runs natively with Cocoa (OS X), GTK+ or Qt (Linux & Windows), in a web browser and even as a command-line application. The developers wrote the core of the program as a library in C (libtransmission) and then the front-ends hook up to it to give the user a nice interface.
Some web development is hard. But getting HTTPS to work isn't, unless your design is terrible. Worse yet, it *was* working better than it is now. Multiple bug reports over months and 1) No Responses + 2) Still Broken.
Developing a client isn't any easier then web development overall. A simple client is easier than a complex website and vice versa. Something that does autoupdates or actively manages files and data isn't simple. GOG barely managed a downloader for Windows. A whole client, much less cross-platform? Hah.
I have ways to mitigate a broken website - plugins, alternate links, etc. I can use Google to search GOG instead of the hilariously broken GOG search. It's annoying and I shouldn't have to, but I can deal with that since GOG obviously can't fix it. I have fewer tools to easily mitigate a program that causes issues in my PC. It's a higher stakes game and GOG has already proven their developers and management can't handle the simple, not-sensitive tasks.
TL;DR GOG devs have failed flagrantly and repeatedly enough that I don't trust homegrown GOG tools.