This is a really underappreciated distinction: the huge difference in capital investment required to develop new inventions in different technical areas. It isn't taken into account in patent law - which sort of makes sense historically because it's a modern phenomenon in both extremes, for software to allow new inventions to be created with so little capital expenditure, and for new inventions in modern pharmaceutical research to require such vast capital expenditure. Such sensitive dependence on technical area for required investment to invent just didn't exist for most of the history of patents. It's a more interesting basis for critical analysis of software patents than simply saying that many software patents cover software that was obvious. That is only an argument that the Patent Office didn't do a good job at fulfilling its proper role under current patent law.