I find that a poor excuse: how can you be sure it works with all browsers if you don’t even try? WebKit browsers don’t do all things correctly and in the other hand have some of their own additions that are currently not in any standard. By targetting, testing and learning with all browsers in mind you get the best overall experience. You don’t do anything with single vendor knowledge in the modern day web.
I know I’m harsh with this opinion, but I really don’t want to see the rise of another IE6 when we’ve just got rid of it. There are already too many live sites out there that fail in random things when not using a WebKit browser and that is a very sad trend to see. So please don’t make stuff that only works with one browser engine unless you’re clearly experimenting with the very latest and greatest.
To keep it short and simple you’re already using SCSS. So you could make a function that makes all the vendor prefixes, which means you’d need to define things once. Then you’d not only learn animations but SCSS as well. Especially how it lets you save a lot of rewriting the same stuff multiple times.
Target all browsers. Be better for the web.