That's just one example, but at the core, that's the difference. You could access Zapmarks on your Kindle browser or your refrigerators smart display if you really wanted to.
That's another difference. With Zapmarks, there is no "most of the time". If you type a keyword you have set up, and hit enter, you will get exactly to where you wanted to be 100% of the time. Once you've got the keywords baked into your brain, accessing them from everywhere is very handy!
In either case, most of the time when I type "n" I get HN or "m" for mail and so forth. I can't really see a good use case for this.