Service Pack or Hotfix Rollup

If you monitor the Ax news on the net, you've probably read that Hotfix Rollup 5 is out.
Pretty fast after Rollup 4, no? Is it me or do these rollups get released more quickly after one another?
And when does Microsoft stop calling it a hotfix rollup, and when does it become a service pack?
The rollup for SP1 is now about 146Mb in size and carries over 350 fixes. (Also note that SP1 was already available end of 2008.)

I have to admit, applying a hotfix rollup does not sound that obtrusive or radical as installing a service pack. You prepare for it, sure. You test it, of course. But you seem to install the rollup faster then a service pack. These rollups don't have the reputation of introducing new problems either.
Maybe that's why...


Edit: Funny note on the side.
From the documentation of this hotfix rollup, the description for hotfix 2130575:

2130575 Assume that you install hotfix 977685. When you click to select the "Select all" check box in the "Create credit note" dialog box, you receive an incorrect error message. However, you do not expect to receive the incorrect error message

When do we expect to receive an incorrect error message? ;-)