Slackware actually has an infinite amount of BoB. Its slackfullness is beyond comprehension. Arch probably has some BoB squirreled away in hidden places, they just don't realize it.
Something not mentioned here is arch's AUR helpers - like yaourt - that automate installing unsupported packages. That means that if you're a more casual user, you can install any one of those 18000 packages with a single command.
This is true. I've always just used yaourt myself, but recently on a new install, I manually installed the yaourt package and realised that manually installing AUR packages is actually really really easy!
Arch Linux: 0 Slackware: 1
Clearly, we have a winner.