All depends upon the size of the browser, the zoom of the browser, the font-size dynamix is set to.
Not a real biggie to get it to always stop at a complete line, but the complication arises if you say resize your browser which changes the math. Now, what page are you on? Do you start displaying the apps based upon assuming you were looking at the top of the page, or were you looking at the bottom.
All in all, easier to give it a set number (25 on computers, 10 on mobile devices).The 25 though admittedly is a hold-over from the previous GUI where 5 across did fit on my screen (when running 1920), but it's a nice round number that didn't bother me in the least