I believe both Holiday Inns still do pretty well despite not being right in the city centre.
The Zoo one is, obviously, next to the zoo which is good for the tourist market. They are right on the Airlink bus route which is another plus, and they have done a good job of making it known that they are on a main bus corridor into town.
Further, they do very well out of events - weddings, conferences etc. It is a big hotel with ample space and decent hospitality facilities. So I believe it will remain a pretty attractive hotel for Edinburgh.
Add to that the fact that Holiday Inn is a known, trusted brand and tends to be pretty reasonable.
Not sure about the Craigleith one as much, but I know it also has decent hospitality/events facilities.