Not only is there IRC, which many people have talked about, there is also chat over XMPP, which is how I prefer to use slack. The alternatives are worse in connectability, because they restrict you to one narrow range of clients and protocols, instead of letting you choose the right client for the job at hand. People use services like slack because they don't want to have to give a shit about communications, they just have something that works.
And you used to be able to get an RSS feed from twitter. Things in walled gardens tend to have a habit of disappearing when interoperability no longer seems to be in the proprietor's interest.
At which point I'll reevaluate the use of the application and potentially move elsewhere. FOSS developers pull these kinds of things all the time as well. Look at the cessation of interoperability after Lennart Poettering decided to "deprecate" consolekit in favor of the non-interoperable systemd. Or they'll stop development of software, like RedHat decided to cease development of the Insight Debugger they gained control of after they bought out Cygnus. The FOSS world is chock full of the same kind of silly, shady underhanded behavior of the rest of the software world.
And you were fully welcome to continue the development of ConsoleKit if you wanted. Slack, on the other hand, can hold all your important logs & metadata hostage.
Completely different situations. Neither of your examples could sanely be described as shady or underhanded - neither of them gave the producer a business advantage it wouldn't otherwise have. FOSS developers don't owe anything to you - they don't have to continue to develop your favourite feature for the rest of their lives. They do however give you the freedom to do that yourself.
