The July Keynote Mobile News & Portal Index offers some insights into Twitter’s recent overhaul of its mobile website, which is aimed at faster and more reliable performance. However, Keynote says that overhaul doesn’t necessarily mean that all mobile devices are reaping the benefits of these changes.

On July 11, Twitter posted details of their mobile web overhaul on the company’s official blog . The intentions of the mobile overhaul were to make Twitter available to more users on both smart and feature phones, and including rural mobile users.

According to Keynote, Twitter followed several of the best practices including: reducing mobile page size; optimizing the mobile site to include less Javascript; increased HTML5 development; and minimizing pages for slower networks

Ken Harker, mobile evangelist at Keynote Systems, said that while the universal mobile experience for Twitter fans has become richer and has expanded its reach, iPhone users have had a different experience.

Keynote’s Index found that for iPhone users Twitter’s site actually increased in size and became 1.3 seconds slower in comparison to last month’s index results. In fact, page sizes increased from 45K to 275K, six times the size it was merely a month ago.

“iPhone users are also now downloading nine images in comparison to two in June and are processing 13 requests for the Twitter homepage, opposed to just four last month,” Harker said.

So what’s the deal?  Harker explains that in order to develop the optimal mobile user experience across mobile devices, Twitter couldn’t do everything for everyone. While feature phones are now able to access Twitter and other smartphone devices are reaping the benefits of lighter pages, the changes reflect differently for different devices. But don’t worry, it’s not all bad news for the iPhone.

“iPhone users may in fact getting a better visual experience with enhanced pages, due to the universal app feel that Twitter has created for its mobile audience,” Harker said. “So while iPhone users may not be winning any Tweet-offs (in speed) anytime soon, they are gaining the benefits of the overall improvements for their total mobile web experience.”

With more than 331 million Twitter users in the United States, and only 32 percent of those being iPhone users, Twitter is fighting a different mobile battle. Twitter seems to have made the business decision favoring a richer user experience for all their mobile users, rather than focusing on a faster experience for a specific set of users.

“It’s important to remember that to meet the needs for a larger user base, your web team may need to determine what you’re willing to give and take from the mobile user experience,” Harker said.

Overall, average page load time was more than two seconds faster in July than the June average at 15.23 seconds down from 17.25 seconds. Average reliability in July was at 99.37 percent, up more than 3 percent from June’s 96.26 percent. Average bytes downloaded, came in at 366.45 KB, down 8 KB from June, average number of objects downloaded is down 2 items at 48 objects from 50 objects downloaded in June.