Bittorrent Chat works differently from Tor. The protocol is not yet finalized but we'll make sure to have external security experts review it to ensure that we deliver on our promise.
Getting to how-easy or how-difficult the installation is, is an endless discussion and is very subjective. One thing that I should add though is that something that might be super easy for you might not be as easy for 99% of Internet users (which is bad for a messaging app specially since you are likely to have friends whom you want to talk to in the 99% category). Installing/configuring a GPG plugin is likely to be one of those.
There are a few issues with using GPG over gtalk, gmail, mail, etc:
1- The metadata still exists. If you use gpg with any email server, the provider of that service knows that YOU contacted someone (and they know who that someone is). They also know "when" this happened. In fact, if metadata is not a concern, there are other much simpler solutions than using GPG. Technically speaking iMessage (or many other messaging apps) should give you the same result (well, if you trust Apple to be doing what they claim to be doing). With Bittorrent Chat, there is none of that. Bittorrent Inc. does not know who is talking to whom at what time.
2- It's difficult to use GPG (or OTR, etc) with your friends who are not technical or just don't want to spend that much time on sending a message. Honestly, I have rarely used it myself because it's just too difficult to get right both on the sending end and the receiving end. A messaging app that intends to be private is not doing a good job if everyone doesn't like it (or don't know how to use it). Privacy should be accessible otherwise people who need it the most, cannot use it.
We are trying to create an app that is not only private but is in fact easier to use than other messaging apps. It has cool features (for technical users as well as non-techies) that everyone understands and can use. People should not have a "private messaging app" that they use for their "private" conversation and one that they use with their "normal conversations". Basically if you cannot say it on Twitter, it's private [to some extent]. Technical people should love it and use it with their non-technical friends and non-technical people should love it because it's just easier to use than other apps (and provides cool features that no other app is).