First, ask what the purpose of GA is: ultimately, it's bottom-line justification is that it helps prove to advertisers just how effective their ad spend is on Google. Use AdWords / AdSense, see how much money you are making per conversion etc., spend more money in a virtuous cycle.

From this perspective, real-time results might not help so much - how long would someone want to run a campaign to see if it was effective, after all?

This being said, I think that even within that context there is a business case. Given the distribution of ad dollars on Google, if P&G or Ford or some other big client was doing huge ad spends, it could be meaningful to tweak things in real-time throughout the day to try to find the best results of A/B/C/.../X tests without wanting any real lag. Now it could be that GA responds faster for certain accounts and this isn't a problem; I wouldn't know first hand one way or another.

I think that conceptualizing the problem from a business perspective helps explain why, for most cases, it isn't important that Google offer a real-time product. But, as we see with Google Instant, there is always room to improve even when things don't appear to be 'compelling' of their own accord!