The chief reason why iPhones don't lag much under normal operation can be attributed to the closed ecosystem. Give a company complete control over the OS and the hardware that's running it and you get ideal optimization (for the most part). Contrast this with Android, an open source operating system that's being made to work on hundreds of different devices with varying hardware configurations and manufacturer-specific UI add-ons. Some Android devices are remarkably good, while others are not.
To everyone else:
For people to say that specs are the only thing matter in the context of this discussion is false. I wouldn't go as far as saying that specs don't matter, but rather, the balancing of technological innovation with usability does...a lot. For companies that truly understand this, a lot more goes on behind the scenes than just slapping the latest silicon into a device and calling it a day. And in all fairness, I think Apple understands this concept more than any Android device manufacturer does. The closest thing we get to this balance on the Android side is the Nexus project, another fine example of why a spec sheet isn't the ONLY thing that matters.
Slamming Apple over their frivolous litigation crusade is one thing, but to immediately jump and pronounce that the iPhone 5 doesn't stand a chance against the current competition because there's "nothing innovative about the hardware" is hearsay. And I'm not even an iPhone user (never owned one).
Getting back to specs and innovation topic, I chose to order an unlocked Galaxy Nexus instead of jumping for an S III to replace my old Epic 4G on Sprint. Why? Consistent developer support is now far more important to me than having the fastest processor and the most RAM. My Epic got a grand total of ONE major system update (Froyo to Gingerbread) since I bought it, and even that came way later than it should have. I had to hack the crap out it (file system conversion, baseband flash, etc.) to get it running CM9's unofficial ICS, but it ran very smoothly up until the day I broke the screen...on two-year old hardware. The very fact that I don't have to fuss with rooting and custom ROMs just to get an Android phone that isn't loaded with garbage and actually does run on the latest that Android has to offer is far more appealing to me than having the flavor-of-the-week powerhouse that might get ONE update. That's just me, anyway...