Modder is spot on. I guess that Firefox and Chrome can be installed on some pretty old computers so the need for the latest hardware is not a big concern - unlike the rapidly moving smartphone market.
While that isn't any guarantee of what the future holds, for me it is enough to make a CB a worthy investment. I figure it is good for at least 3 years, and the fact that cr48s are being upgraded to the latest versions is a really encouraging sign as they have half the CPU of the current machines.
Even smartphone development has slowed to the point that there isn't really anything on the market to tempt me from my >12 months old HTC desire.
The new HTML 5 standard is just about to cause a revolution on the web. We've already seen a few sites start to use it, but it will be a few years before it really takes hold. I work in this industry and can see the benefits it brings, and am very excited by it. As the chrome browser and chromeos support this standard today, I'm fairly happy that right now they are as futureproof as it gets.
The thing that is more likely to change is the way you connect - wifi and 3G will be replaced with 4G, wimax, and the new 'white space' stuff. This shouldn't make a huge difference to a CB providing you can get a smartphone a wifi hotspot app.