Yes, spring is a slow period for Apple (AAPL) and its fiscal third-quarter results reflected that. It was that way last year as well because the new iPhone debuts in the autumn. But how rapidly has Apple’s annualized sales growth slowed down since last spring? Real quick.

In the spring of 2011, Apple racked up 63-71% sales growth in the Americas, Europe and Japan. Asia-Pacific growth clocked in at a torrid 240% as the iPhone found important new distribution channels. Everyone knew that those growth rates simply had to come down, but the speed of the slowdown is a shock.

Europe’s annualized revenue growth was merely 17% in the spring of 2012. Growth in Americas was 26% and growth in Asia-Pacific 25%.

Those are healthy numbers. But here’s the kicker: just one quarter earlier, Japan growth topped 90% and Asia-Pacific 110%. Americas and Europe were still growing at better than 40% each.

So not only is Apple falling off its March quarter growth faster than expected, the rapid cooling is evident simultaneously in North America, Europe and Asia — all major regions, even though Europe clearly is suffering worst due to its latest financial convulsions. This just might be an old-fashioned maturing of a business globally. You cannot blame this miss on seasonal factors, because what matters here are the year-on-year comparisons – and the iPhone aged as rapidly this year as it did last year.

Or did it? Perhaps the phenomenal strength of the Samsung Galaxy S III in June and July finally dented Apple’s smartphone momentum measurably. Samsung hit the 10 million unit sales mark in two months this summer, much faster than what the previous Galaxy managed — it took the Galaxy S II six months to hit that mark.

The autumn quarter will be simply fascinating, particularly if the next iPhone hits the stores after the quarter closes. Apple is now facing the Skylla and Charybdis of the European debt crisis and Samsung’s emergence as a real rival. We may well finally see some real iPhone price aggression from Apple in emerging markets come next winter.