It's important to differentiate between the file format and software that renders that file format. Admittedly there are better and worse PDF viewers, but that shouldn't be the final (or even most important) determiner of how important it is.
Yes, I often use SumatraPDF, but there's always those super-complicated Turing-complete documents which use web-based-aunthenticated-signed God-knows-what, that won't open in anything other than Acrobat.