Staying power: iPhone 5, iPad 2 still Apple's most popular models

The iPhone 5 and iPad 2 remain the most popular models among consumers, says a new report.

Looking at the number of iPhone models detected on its mobile network, Localytics pegged the iPhone 5 at a 27 percent share followed by last year's iPhone 5S with a 25 percent share. That left the iPhone 4S in third place with 21 percent, the iPhone 4 with 13 percent, the iPhone 5C with just 8 percent, and other assorted iPhone models with 5 percent.

Why would an earlier iPhone model still be the most popular, even just by a slim margin? Much of that may be the result of the standard carrier contract that locks a customer into a phone for a solid two years. With the iPhone 5 proving a hot commodity after its release in 2012, many mobile customers would likely feel compelled to hang onto the phone until later this year, which means they'd bypass the 5S as they await this year's model.

Still, the 5S was no slouch as it accounted for a quarter of all iPhone traffic. And gazing into the future, the iPhone 5's share will surely take a nosedive after the iPhone 6 -- widely expected to be introduced Tuesday -- has gained some traction.

For now, though, the iPhone 5 found itself in the top spot even though it's no longer up for sale via Apple. The iPhone 4 may have scored third place because it's available for free with a two-year agreement.

Among Apple's tablet lineup, the iPad 2 garnered the lion's share of Localytics' iPad traffic with a 29 percent share. That's an impressive number given that the second-generation iPad will celebrate its fourth birthday come next March.

The original iPad Mini took second place with a 20 percent share, followed by the iPad 4 with 15 percent, the iPad 3 with 13 percent, the iPad Air with 12 percent, the original iPad with 6 percent, and the iPad Mini with Retina with just 5 percent.

Why do the older iPads have more staying power, as Localytics puts it? There are at least a few reasons.

First, the iPad 2 was available for sale from Apple until March 2014, so consumers had plenty of time to snatch one up following its debut in March 2011. Second, unlike iPhone buyers, tablet buyers aren't locked into any contract. So there may be less incentive to upgrade to the latest and greatest model after two years. Third, except for a sharper screen, Siri support, a faster processor, and a few other enhancements, the later iPads don't boast a huge number of must-have features over the iPad 2. So owners of the second-generation model may be more content to simply hold onto what they've got.

A similar scenario likely holds true for the iPad Mini, which was the third most popular model. Offering a Retina Display as its only significant selling point, the second-generation Mini showed up last on Localytics' list. Of course, the original Mini has been around a year longer than its predecessor and is still available for sale via Apple for $100 less than the newer model.

Speculation has surfaced as to what Apple may do this year to refresh its iPad line. Apple's tablet is still popular but has increasingly lost market share to Android rivals. And will Apple announce a new iPad at Tuesday's launch event or wait until the traditional October time frame?

"Though history suggests that Apple will announce new iPads in late October, it will be interesting to see if Apple continues this annual trend given the stickiness of older models," Localytics said. "There are currently four iPads on sale on the Apple website: the iPad (4th gen), which was re-launched in March 2014 when the iPad 2 was discontinued, the iPad Air, iPad Mini, and iPad Mini (2nd gen).

Localytics analyzes the use of mobile and Web apps across more than 1.5 billion devices and 28,000 specific apps to determine the share of mobile devices. For this latest report, the firm looked at more than 100 million iPhones and iPads over the entire month of August.

CNET will host a live blog of Apple's launch event on Tuesday, September 9, starting at 10 a.m. PT following a broadcast preview of what's to come at 8:45 a.m.