The universe of devices, even so-called "smart" devices, is endless. It has facets that nobody has yet conceived, and other facets that somebody has conceived but has not yet brought to market. Yet companies, organizations, and bloggers desperately want to limit that universe significantly to promote the ability to have a "consistent user experience" across devices.
As a simple example, consider user input. Right now, most phones have either a keypad with a scroll control, or a stylus input. There might be a limited-functionality speech input. The industry has created user interfaces that assume one of these input types. Dozens of companies have gone through a lot of effort to make typing on these devices easier by making better keypads or by adding a variety of predictive typing software. But this set of input mechanisms is much smaller than it will be even in the next year or two.
There's nothing particularly magic about these two types of input mechanisms. They both have histories that have little to do with the way devices are used today. Smart people are inventing alternatives. Samsung, among others, is working with accelerometers for spatial gestures as a input mechanism. It is currently possible to drive an entire user interface on a phone - including web and some Java - with speech. Fingerprint scanners are cheap. Interface gloves are possible. While none of these currently provides a satisfactory user experience, some probably will in the future.
Now, if I could write an application that ran natively on Palm, Symbian, and PocketPC without recoding, I'd do it. Java is an entirely imperfect answer, but it moves us partway there. But I would never expect this application to run on a scroll-and-keypad device without some redesign. And I certainly wouldn't expect it to work for a speech user interface.
It's possible to achieve a "consistent user experience" across multiple devices, but only if you sacrifice innovation and user experience, or if you very loosely define "consistent". I'm hoping for the latter. Let's not limit what we could do to create an artificial consistency.