Are there any Linux Distro that features a Tiling Window Manager as main WM?

I don't believe there is. The reason for this is probably that people that use tiling window managers tend to be a) quite technically proficient, and b) tend towards minimalism—or exacting standards of control over their setups.

Neither of these two conditions lends themselves naturally to pre-built solutions.

If your window manager of choice is dwm, for example, why would you want to install a distro where someone else had made the majority of the decisions about the packages, environment etc for you?

You would be much better off with a minimal install of your base distro and configuring everything else yourself – which undermines the rationale for a tiling distribution.

Salix Ratpoison 13.37 is released! This is probably the first ever linux distribution release featuring Ratpoison as the main window manager. The aim of the Ratpoison edition is to create a system that is fully usable with the keyboard only...

(via http://www.linux.org.ru/news/slackware/6856589 (a news item, in Russian))

Salix OS is a derivative of Slackware (via Zenwalk), as explained in the news item where I've read about it.

Your best bet is to go for a "minimal install" of your favorite distro and then "build up" from there. A few distros I have used that offer minimalist installations:

• Arch Linux would actually be perfect for the minimalist approach as you only install what you want (and dependencies). Awesome, Scrotwm, dwm xmonad, and other tiling WM are available either in community, extra or the AUR
• Ubuntu offers an alternative download
• The OpenSuSE DVD has a "minimal X" installation