Are people really buying it at full price?
While not impossible I think it's safe to say no.
I haven't bothered looking at in-stock numbers, but I have to wonder if R&S factory installs the options, or if its at the distributor (I assume they didn't pass that to the customer to do, but again, really lean would drive that to be). Based on lean manufacturing and other similar drives to have as little on-hand inventory, it would make sense, both for R&S and for the distributor to only have a few physical pieces of inventory on hand as possible (less money tied up in stock, better inventory turns). If so, then all the RTB2002s could be a pool and all the RTB2004s could be another. EDIT: I guess actually 4 pools, since I think the MSO is a physical option? I forget that this scope also comes without it right? Also having just 4 pools greatly reduces errors of trying to figure out and send the right scope with all the right options to the right customer. Far easier to grab 1 of 4 (2 no mso, 2 mso, 4, no mso, 4 mso) then tossing in the product codes for the bandwidth and decodes, and then final ship. (While my company doesn't make scopes, we basically do the same thing, custom configure at setup so we only have to have 1 model, and in our case 2 optional pieces installed by field service at setup plus software.. granted we physically setup all our instruments for customers, but you'd expect that for a 7 figure device.)
But also could be as stated, people getting the better deal on the down-low, or simply buying the regular scope with the exact same options as the fully loaded, for the new list price of $6k instead of $8k.