Sony's Playstation was the sole home of the Tenchu series for quite some time; another one of those "exclusives" that the big black box would never see.
The gaming landscape is a bit different now. It appears that the latest trend is uni-platform releases, sometimes even when an exclusive was a part of the original plan (cough, GTA, cough, cough Assassin's Creed).
The acquiring of the Tenchu license from Sony immediately meant that the stealth/action series was open to all consoles, including the Xbox. With Tenchu: Return from Darkness doing just so-so on the Xbox, and with a general lack of interest from gamers in the franchise, Activision bailed and left the ball in FROM's court. It's taken a bit of time, but yes, we actually have a Tenchu game coming to the Xbox 360 in June.
Tenchu Z is the next-gen version of this long-running series, but a quick glance at the demo will make it abundantly clear that most of the dev team's energy has gone into the gameplay programming. There's the typical Tenchu clip, the blurry background textures, and even some animations that look ported straight from earlier iterations of the series. Yes, Tenchu Z is a bit visually disappointing in this demo, but hopefully things will somehow be a bit different in the final version.