With the NSA at least theoretically we have congressional oversight. The same can't be said for Google and most of the other companies we trust with our data. Their level of access may be comparable with the NSA but there are few if any legal protections or opportunities for oversight. If the same abuses were happening, they might never come to light. With the big companies, we might only ever be able to speculate.
Google employees that become whistle-blowers don't have to face the same adversity as government employees that become whistle-blowers. It's also easier to sue Google than it is to sue agencies like the NSA.
