Apple sold 5 million iPhone 5s in its first weekend – a company record. But some people expected more, and now have to explain why Apple didn’t top their predictions. In reality, this isn’t that big a deal. The rest of the year matters a lot more.

Compared to last year’s iPhone 4S launch, when Apple sold 4 million phones, 25% growth may seem disappointing. This is Apple, after all, and Wall Street is used to seeing the company blow past expectations, not come up short. (The iPhone 4S launch, if you recall, was more than twice as big as the iPhone 4 launch.) This number isn’t 10 million or even 8 million or 6 million, so some are saying that it’s “WORSE THAN EXPECTED” or “very disappointing”.

So, yes, 5 million sales is below some estimates. But that really doesn’t mean much in the long run. Why not?

First, for the real story, you need to think about supply and demand, and once again, demand surpassed supply. Apple stopped taking launch weekend pre-orders after only a short period of time, and many stores were sold out of various iPhone models throughout the weekend. We still don’t know how many iPhones Apple could have sold over the first weekend if it had unlimited supply, and we may never.

Next, mobile is a complicated industry, where 2-year contracts often dictate purchase decisions. Apple sold almost twice as many phones over the past four quarters than it did the four quarters before that. Few of those people are already eligible to buy an iPhone 5 at a subsidized rate — it’ll be months before they can justify buying iPhone 5s. Anecdotally, I’ve also seen mentions that AT&T was being stingier about early upgrades this year than last year.

Further, first-weekend sales just aren’t that important relative to an iPhone’s lifetime sales. For example, the 4 million iPhone 4Ss Apple sold on launch weekend last year represent just 3.5% of all iPhone shipments over the past four quarters. The 1.7 million iPhone 4s Apple sold opening weekend represented just 2.2% of the phones it would sell over five quarters before launching the iPhone 4S. It’s nice for Apple to sell 5 million iPhones in a weekend, but it’ll be more impressive if it can sell 200 million phones over the next year.

Long story short: It’s a fun press release to see from Apple every year, but the iPhone 5’s real sales performance will be measured in months, quarters, and maybe even years, not weekends. It’s still crucial for Apple to sell a lot of them, but late-December sales will be a lot more important than mid-September sales.

iPhone 5 line photo (cc) Blake Patterson via Flickr. Portions of this article were originally posted at SplatF.