Free apps do well on Android. Paid apps (Outright & Free + In App Purchases) generate more revenue on iOS. Being able to show traction is important for startups but, being able to show increased revenue is equally if not more important.
Until Android on a whole proves to be more lucrative to monetize apps, many developers will continue building iOS first (imho).
Your statement is true, but sort of missing the point of the article. Sure, "many" developers "will" wait "until" Android "proves" better. But some won't, and there is value in being part of the early ones to jump. The article is advocating jumping now and gives some arguments (not all of them convincing IMHO) as to why that's a good idea.
You're just saying that not everyone will take the advice. Well, yeah. :)
Until Android on a whole proves to be more lucrative to monetize apps, many developers will continue building iOS first (imho).