I have read numerous interview with Ged over the years and here is my recollection:
Geddy bought a old used Fender Jazz in the early 70's. He used it for the first RUSH album. Once the band cought on, the record company (Mercury) paid for them to get better instruments. Geddy got a 4001 because it was what his heros were playing (Chris Squire, etc.). Geddy played the RIC 4001 (and some 4002s and 4080s) for the rest of the 70s.
While recording Moving Pictures, Geddy was looking to change his sound around and was trying to get a different feel. He pulled out the Jazz and used it on several tracks. In fact, he used the Jazz on all the tracks except "Red Barchetta" and "The Camera Eye" with which he still used the RIC 4001.
My understanding is that Ged used the Rickenbacker 4001 for Signals as well as part of Grace Under Pressure. With GUP, Ged was looking for a more new wave style and ended up using the Steinberger on the tour.
With Power Windoes, producer Peter Collins had a Wal Bass and talked Geddy into using it. Geddy like the sound and used it for a couple tours. But after a while, it was too heavy for his aging back. So by Roll the Bones, Geddy had returned to his old Jazz because it was lighter.
Now granted, the Jazz is nice, but no way is it lighter than the Steinberger, so that cannot be the only reason. I suspect that the fact that Fender has a Geddy Lee model out there is the main reason now. I suspect that contractually, in order for Fender to continue to pay Geddy for his sponsership, Geddy has to be seen playing his Jazz a certain percentage of the time. Hence the use of the the RIC 4001 for just one song.
