Experienced investors never take GAAP at face value - most of them will work with both the GAAP and pro forma (as well as any other public releases) and try to reverse engineer the individual lines in order to tease out more pertinent (in their opinion) factors that affect the value of the business. different investors value risks differently but the pro forma is created by management for a general set of investors in order to bridge the gap between GAAP and exact economic reality.
As a side note, GAAP definitely isn't industry agnostic. For example, FASB (the financial accounting standards boards) issues guidance on revenue recognition for all sorts of companies and the guidance for a software company is very different than the guidance for your generic widget manufacturer.