Actually we don't guarantee revenue, we only guarantee upvotes. Whether those convert into revenue at payout is beyond our control. We have always resisted making promises of actual returns, and when estimates have been given, they are always given as depending on STEEM price and reward pool behavior.
In fact, the earliest criticisms raised by whales were because we did not guarantee any level of returns.
SBI is more like earmarking SP for dedicated support of accounts you choose. We can't guarantee that the support has any value, any more than you can guarantee that an upvote on this comment will have any value after it gets countered by mmkk. In most cases the support will have value, of course.
