I may be confused about what cloud hosting really is...

I asked Rackspace how its Cloud Server (CS) 256MB/10GB compares to Slicehost's 256slice VPS, and they said it's exactly the same (only different billing and BW). I know they are the same company.

So, why do they call it Cloud Server? Isn't it just a collection of VPS (virtual private servers)?

For me, cloud hosting would be: if I need any additional horsepower at any given time, the cloud would automatically stack more VPS and then charge me at the end of the month for the surplus of resources. Reading Rackspace's info, it looks like it's for me to decide when to stack more CS and that its Cloud Servers don't AUTOMATICLY scale up.

Am I confusing things?