I think you're right that comparing to profit isn't right, but I still contend that comparing to revenue isn't either. What I meant is looking at per-unit profit margins (i.e. excluding things like R&D) - if just producing whatever they're selling costs 99% of revenue generated from it, then 5% of revenue on R&D looks pretty high - they're drawing on capital to do so. If, on the other hand, those costs are only 5%, then they're stashing away an enormous portion of revenue despite R&D and thus they're R&D spend looks pretty low.