Here’s my quick view on the two strategies:
In the words of Agent Jay:
Old and busted: pages and technologies that work for older browsers
New hotness: think AJAX
Both strategies have the same end goal: provide support for the widest variety of user agents, but have opposite approaches of doing so.
More reading
This is a quick high level overview, so read below for more information and examples:
Joel
about 1 year ago
Heh – I actually discussed this at the Google Developer Day with the guy at the helm of the Gears project. Was more wrt GWT but it was interesting nonetheless.
Your image sums up exactly my thoughts on the words (and kinda how one approaches it – hence I prefer Progressive Enhancement, but that's just me o=))