User blog comment:Deshiba/Team Frost - an overhaul./@comment-5980721-20130212171021/@comment-4022742-20130212171958

Oh because champions like Irelia and trundle easilly reach over 60% reduction from tenacity with an 80-90% against slows specifically with boots of speed and Relentless...

Which would be rediculously OP against champions who rely on the slow passive to tie into the rest of their kit. This is currently a problem RIOT themselves is looking at with Sejuanni, it is actually their idea to make seju's slow an unaffected by tenacity mark.