Actually Apple did share it in advance with Adobe and Autodeskmaybe more. Some devs that were thinking ahead, such as Panic, have already built in retina support for apps like Coda 2. Google quickly busted out a Canary release of Chrome including retina support. So hopefully it won't take ages!
Now as for retina-ready websites, I don't think it's a huge priority right now for most designers. I'm just now learning about how to do it. Most of us build our sites as a PSD first with a working space of around 960px wide. So we would have to remake all our PSD files with twice the resolution. Good thing Apple released this new machine as it will let us design 1:1 retina for The New iPad and the RMBP.
However there are a couple problems. The content (images) will need to be higher quality. So I don't think there will be any retroactive up scaling of old website content. Only new stuff going forward (though sometimes getting a quality image from a client for use on their website is nearly impossible!). So you end up with "the old web" showing low-res images, and the "new web" which is sharp as a tack. It may become readily apparent years from now if, say, an article you're looking at was pre-2013 or post-2013. Furthermore this adds in content complications. Most artists don't have a problem including small web versions of their work online because even if stolen they don't actually have the quality for anything to be made of them. But with retina we're talking about print (or near print) quality. So the images could be jacked and printed easily. How can we lock down images online? It's impossible right now.
Bottom line it will probably be a while before most websites are retina. And some may never be retina or take a decade to switch. But with Windoes 8 providing better retina support, combined with iPad popularity, we will hopefully see it sooner rather than later. I predict most pro apps will be updated within a few months. Good devs that care will have it in 3-6 months. Most apps that are updated every once in a while will have it in 12-18 months.
As for web retina timelines, I think most tech sites and pro portfolio sites will be the first retina ones to roll out. I think we've seen some of this happen with the retina iPad. So give it a couple months for that. Next major companies like Target, Best Buy, Amazon, etc will probably begin support within 6-12 months. Then smaller business sites that care somewhat about design 12-24 months. 2-4 years out most ordinary sites that don't care much will probably go retina simply as a result of the redesign cycle. So whenever they redesign they'll just happen to get it as most packages will probably offer it standardespecially as retina displays start pushing into the 20-30% marketshare range. I'm talking about PCs, generic tablets, iPads and Macs.You don't want your online store to look like garbage to part of your customers for two reasons: your competitor has a beautiful retina site, and the early retina users probably have more income to spend at your store!
This is quite the complex, multi-faceted issue. I hope it doesn't get botched somehow. But Apple is really pushing the industry forward. It's usually inevitable that the industry will push back for a while. We've seen it with many things, such as Flash. Now even Adobe seems to be moving on, and I don't know any designers (or have had any clients inquire about) making Flash websites.
