Rewind to last week, if you will. On Tuesday, after the “Let’s Talk iPhone” event that has now been analyzed to death, it sunk in that Apple’s revolutionary Siri personal assistant wasn’t an iOS 5 feature, but an iPhone 4S feature. Was it due to hardware limitations, or marketing? Now that reports are coming in that the 4S totes 512MB of RAM, it’s getting harder to say that this was entirely a hardware-based decision.Those who follow Apple and tech news have known for some time that the company would be delivering voice recognition technology in iOS 5. When the firmware update was first detailed in early June, there was no mention of the Nuance-powered feature. Most of us concluded that this was because Siri wasn’t quite ready for showcasing. But now we know why it was held back – it was set to be an exclusive for the next iPhone, rather than a universal iOS 5 feature.It’s quite possible that Siri couldn’t run up to Apple’s standards of smoothness on other iOS devices. The A5 chip powering the iPhone 4S is a big leap forward from the A4 inside of the iPhone 4 and iPad 1. Perhaps they didn’t want to compromise the experience for us with a laggy, choppy, or slow Siri. Perhaps.But what about the iPad 2? With the revelation that the 4S probably carries 512MB of RAM under the hood (as reported by TUAW and several other sites), this makes the engines of the two devices more or less identical. Both have the A5 chip, and both have identical RAM. Therefore, if Siri can run up to Apple’s standards on the iPhone 4S, it should be able to do the same on the iPad 2. Yet there has been no mention of the personal assistant on Apple’s tablet. What’s up with that?Even incremental Apple hardware updates need a killer feature. Sure, with the iPhone 4S being roughly twice as fast as the iPhone 4, and a phenomenal 8MP camera in tow, its performance should see a huge boost over the 2010 model. But those specs lack that certain draw that gets people excited and gives them that extra itch to upgrade early. Just ask Android tablet makers how specs alone fare in selling a product.Siri, on the other hand, is like nothing we’ve ever seen before. It answers your questions, even when spoken in a conversational tone. It works with a variety of iOS apps to perform common tasks by simply telling it to. It blurs the line between speech recognition and artificial intelligence. Siri can be the kind of killer feature that the iPhone 4S needs.If the iPhone 4 and the iPad 2 got Siri along with iOS 5, then the iPhone 4S could have conceivably been Apple’s most boring update in years. Not weak, mind you, but lacking sizzle. But with Siri, while the latest iPhone may not be the revolutionary iPhone 5 that many were pining for, it still has at least one feature that’s revolutionary.It could be argued that Siri hasn’t been made available for the iPad because speech recognition lends itself more to a phone than a tablet. This makes sense, to some degree. Tablets are more often used in a comfortable environment, when there is nothing to keep you from leisurely browsing for information on the beautiful 9.7 inch display. Phones, meanwhile, are used more while walking, driving, or in a pinch. These are the times when Siri makes the most sense.So I won’t take the hard line that Apple definitely tied Siri to the 4S strictly for marketing. It could be that older devices just wouldn’t be up to snuff, and that the iPad 2 doesn’t need it all that badly. But I will say that – at the very least – it’s extremely convenient for them to have it exclusive to the iPhone 4S, which is otherwise lacking in “magical” new features.