No, you are incorrect. Slicehost technology is Rackspace Cloud Servers technology. Cloud servers and Slicehost slices are running in the same racks on the same hardware using identical technology stacks -- always have been. The control panel for managing a Rackspace Cloud account and products (including servers) is distinct from the Slicehost customer control panel, and the support teams were distinct groups of people. Now these two corporate structures and logical pools of resources will simply be merged under the name Rackspace Cloud Servers.
Oh, forgot to point out the other big difference. Slicehost had (and still has) a monthly billing model with a monthly bandwidth allowance bundled into the cost. Rackspace Cloud Servers costs are calculated on two factors: how many hours the Cloud Server ran that month (from the day/time you instantiated it); AND then bandwidth usage is calculated separately, based on some $$/GB rate:
So, the real point is that even if this wasn't apparent to you the customer, the substantial differences between Cloud Servers and Slices was branding and different pricing models; the support teams were also separate (and the two front-line support teams have different "styles"). Otherwise, behind the scenes, they're literally the same thing -- in terms of data centers, hardware platforms and hypervisors, etc., etc.
This is what I was looking for in this thread, so thank you.
The email left me concerned of the transition and what it would mean for uptime of websites, but if it's literally just a change of billing, branding, and control panel, why are they waiting months and months to change this? If it doesn't affect my websites' uptimes or IPs, they should just rip off the bandaid now.