Why do migrated machines get a new IP?

EDIT: The IP address didn't change in the first place. Well, now this question doesn't make any sense anymore. It can be deleted.

Hi Linoders,

I've recently downgraded my Linode (unfortunately, but I wasn't using the Linode enough).

During that process I got a new IP address assigned to my VPS. The question is: Why?

I thought that the IP points towards a dedicated machine that holds the assigned VPS. Something like:

Paul's Mac -> WWW -> Hurricane Electrics -> Linode Rack -> Linode Server -> My VPS

Maybe I don't know enough about virtualization but couldn't the "Linode Rack" (I simply don't know how this part/software is called) assign a new machine to the same IP? Like a dynamic sort-of-DNS system? Or do they do hard-linking so that each new dedicated machine gets a fixed pool/range of IPs?

In general, I just want to ask: Why a new IP?

Thanks (for answering this weird question :))!

Paul