The true killer feature of Sublime Text is the fact that it runs
flawlessly on the 3 major platforms (Windows, OS X, Linux).
I know people will scream that Emacs (and vim) have windows ports, but they are utter crap compared to running them under a Unix. I can tell that from experience. Emacs on Windows is unbearably slow: it took 10 times as much to start as on the same host, same SSD, when it is run under a Linux VM! It also relies heavily on standard Unix tools (wget, grep, ...), whose ports for Windows are extremely outdated to the point that they are unusable (Emacs 24's find in file relies on features not provided by the standard non-CYGWIN grep). There only solution is to use CYGWIN, which is a mess: it's extremely slow, behaves weirdly (wrt path names, notably), and it doesn't play well if you already have a standard MSYSGit installation for your git needs. (I have tried using Emacs at least 4 times already, and I have never managed to stick to it, for these kind of reasons.)
I love ST. It boots fast, is gorgeous, modern (unlike Emacs, you can have your cursor outside the region you are viewing!), trivial to configure (with auto-reload of config files), has sane defaults and great support for most languages out of the box, it has a great community, and a nice language choice for moddability. It might have been born has an OS X éditeur du jour, but I'd say it's more of a blessing for Windows developers where good, modern editors are rare.