Lightroom's Develop module
is ACR, so you like ACR too.
I understand they are built off of the same engines, one is a freestanding program and the other is a photoshop plugin, correct?
Plug-ins are not Adobe software.
You can't buy CS5 without Camera Raw (ACR), and you can't buy Lightroom without the Develope module (ACR).
Photoshop Lightroom was designed for photographers that had a substantial image database to manage and monitize. Lightroom is intended as a compliment to Photoshop CS, not as a replacement for CS, which is why Lightroom's primary function is database management, not image editing.
Lightroom was first released as Mac-only public Beta in January of 2006. Lightroom started shipping in February of 2007.
Note that the Lightroom
3 Develope module, uses ACR
6. Camera Raw has been around since PS7 (August 2002)