This is exactly my experience: people will generally pay for convenience or simply because they like what you're doing.
I develop a GPL'd e-reader app for Android (obligatory self-promotion link), and at first I considered the model described in the article... I finally went a slightly different route. I have 3 versions:
1. The classic OSS version, which is a straight Maven build from the sources at Github. You can get this from the downloads page on the site and from the FDroid Market. FDroid actually build the binaries they distribute from source themselves.
2. An ad-supported version in the Google Play Market
3. A 'pro' version in the Google Play market, which is paid.
The difference between the 3 versions is access to our synchronization servers. You need an access key to use this service, and the classic version has a preference field where you can enter that key. I give out keys to people that contribute translations or help the project in any other way and you can buy them for the same price as the Pro version.
The 2 versions in the Android market have a key built-in, and lack the Preference field to enter one. That's the only difference though.
All versions are GPL'ed with the sources for the classic version directly available from Github, and the patches to create Pro and Ad-supported available on request by e-mail.
So far this model actually worked pretty well... I'm nowhere near being able to quit my day-job, but I make in enough in donations / sales to pay for the hosting and maybe an occasional test-device.