As I recall from my OS X days, some .plist files are pre-tokenized or -parsed binary files. Quicklook apparently knows how to tell the difference, and un-tokenizes it before showing it to you; whereas a generic text editor like Sublime Text will load the raw contents.
Try loading the same file into another generic text editor, such as 'vim', and see if you don't get the same results.
Also: See the man page for the plutil(1) command, which does the conversion.