In 2012, Samsung promised the Android 4.1 update for the Galaxy S2, and said it would come sometime in November. Then they had some issues, and said it's coming in February 2013. That got delayed, too, and most people only got it at the end of spring. Then Samsung insiders also leaked out that Android 4.2, and even Android 5.0 , will be coming to Galaxy S2, too.
But now you can forget about all of that, because it seems Samsung has run into some major issues with Touchwiz for Android 4.2, and apparently Android 4.1.2 will be the last update for the Galaxy S2. This means the Galaxy S2 will have only received 2 major versions of Android - 4.0 and 4.1, in almost 2 years.
Yes, in a way Samsung has respected that "pact" Google made a while ago with some OEM's, that said they should upgrade the devices for 18 months. But Google releases 3 major upgrades in those 18 months, and this was more like 24 months anyway. So I think the Galaxy S2 deserved to get at least Android 4.2, or since they were going to start working on it so late, they could've just skipped it and jumped to Android 4.3. I'm sure Galaxy S2 users wouldn't mind. It seems less likely it would've received KLP, too, though, if it's indeed going to be another major overhaul the way Android 4.0 was.
In a way, Galaxy S2 aren't losing that much. Both Android 4.2 and Android 4.2 are pretty low on features that they've added. You're losing the Photosphere, and the big settings toggles (although Touchwiz has pretty much had that covered for a while), and the ability to have widgets on your lockscreen, like Dashclock. In Android 4.3 you're mainly losing some security features, and that's only if you believe they would've skipped Android 4.2 for it.
Samsung hasn't been too bad with updates in general, although Touchwiz does make them quite slow to upgrade. I think with Motorola starting to use near stock Android for Moto X, and many other devices after that, and with Nexus devices becoming increasingly more popular, it's only a matter of time before more people will start preferring stock Android over anything else, and will begin to demand that Samsung uses it on its real flagship models (yes, Galaxy S4 had a Google Play Edition, but is Samsung really going to promote that one?).