Consider Veigar, one of the oldest and most purely assassin-style characters in the game.
Would you consider building CDR on him? Perhaps, but only because I want to spam my Q early game. This is the only reason anyone should ever build CDR on Veigar. Everyone and their baby sister knows that veigar is meant to grab a DFG and stack up AP PRONTO. You're goal in every single encounter is to catch the enemy mage/squishy in a stun, curb stomp them in .023 milliseconds, and walk away ALL BEFORE YOU'RE W HITS!!! You want to play a Veigar that has CDR vs more AP/utility? That's fine, but it's sure as hell not optimal.
That said, you want an AD Assassin in Pantheon and Talon? You should be asking for items that help you get massive burst off really fast and then escape before you get caught.
OH WAIT!
ICWATUDIDTHARRIOT: See SotD, Mercurial Scepter, BT, and maybe Frozen Fist. That's a beautiful build guys!
And please, stop comparing Riven(painful bruiser) to Talon(sexy assassin). They're different. Different galaxies even. Just.....well I think you see what I'm getting at.

Please quit whining about what you don't understand. Riot has done a fantastic job so far, and Morello has already mentioned that these new items are just the completed and experimental ideas. There's plenty more talent/creativity/engenuity over at Riot Games that they'll be drawing from for even more cool items in the near future.

And if you don't understand or just outright don't like the items, you can at least be polite in your opinion. Or kindly go **** yourself.

But veigar isnt a ad assassin, your title doesn't match D:


Edit: ad assassins dont auto attack as much, therefore dont benefit from crit chance which means bt>ie.

More skills spammable = more damage, since they dont aa as much as adcs.

If you can fit it in your build without harming it's effectiveness, CDR is amazing on pretty much everyone except for say like, Udyr.