The only plausible counter-example I can think of off-hand is .NET. But even there, it started out not as a new from-scratch platform, but basically as a clone of Java with some windows-specific bits thrown in. So maybe a billion is enough if you're just trying to compete, not innovate.
Something to ask about your company: are you going out to find customers, or are they coming to you? If it's the latter, congratulations; you've succeeded where thousands of entrepreneurs have failed. But if you have to make lots of sales calls to close that one sale, it doesn't necessarily mean anything, even if you're profitable. Try enough prospects and one is bound to say yes, if only because they have money to burn and want to see if you can help them out. That was a lesson learned at my last employer, which was profitable before I joined but got no new business while I was there, because their revenue came from customers that didn't really use the product and just bought it because a couple million is a drop in the bucket when you manage a few billion in capital.