Sorry, but I'm not familiar with this – could you share more please?

It has subsequently been increased to 10.

TIL it's now 10 devices...

I think the idea is that you don't tie all your friends' devices to your account to share apps etc., but I am just guessing.

Quick search reveals that up to 5 devices can be tied to the same Apple account: https://discussions.apple.com/thread/8030144

What is lost when they make Pidgin available on the App Store (under the restrictive App Store license) + under GPL (on their website) as opposed to not having an App Store version in the first place and releasing under the GPL only?

I don't see how the presence of a second, more restrictive license invalidates the GPL given that anyone willing to take advantage of something not allowed under the more restrictive license can still do so under GPL?

It's either GPL with all the rights that entails, or you can't (legally) redistribute it at all.

Now, if you own the copyright you can give out as many parallel licenses as you want. But pidgin & libpurple have been around for 20 or more years and have had many, many contributors, and they have to explicitly give up their copyright or consent to the license change to do what you propose. That's theoretically not impossible, but it's a lot of work.

This is why some projects require you to sign copyright-assignment agreement before they will take your patches—it gives the project more flexibility to change the license in the future.

There are many ways to skin this cat.

It's not a commercial project with a CLA, it doesn't have a single owner, many of the people who contributed major parts have moved on or would object to a license change from copyleft to permissive, so it's not a matter of "just change" the license. And libpurple is the real meat of the project.

I followed a few of the developers for a bit as I really wanted to work there. I believed they got aquired into the g+ team (gchat? maybe?).