I'm not talking about software, I'm talking about information. Information shouldn't have an expiration date. Here's a webpage from 1994: http://www.lysator.liu.se/pinball/expo/ Surely you wouldn't prefer a world where the blog you wrote 4 years ago can't be viewed on a new computer?
Also worth pointing out it's much easier to display old formats than it is to make them editable.
IMG tags with unquoted SRC attributes, and unquoted ALIGN attribute
BASE tag with default attribute - tag is: <base="http://www.lysator.liu.se/pinball/expo/"> but should be <base href="http://www.lysator.liu.se/pinball/expo/">
UL tags with no LI tags
So yes, under some circumstances, old formats are deprecated - even on the web. The world is better for it, but it still sucks for those who need that old stuff and are unable to move it forward.
It's a good thing that webpage didn't use the <blink> element.
A counter argument to that, is I'm not sure if I want to live in a world where parsing an HTML document takes over 1,000,000 lines of unparallelizable C. You are sweeping a huge requirement that makes the rendering of that page possible in 2014. Ultimately it takes software to render that information, and the software that does render that, may have an expiration date.
How about if we're talking a blog I wrote 20 years ago, vs. some really nice improvement in modern software?
Backwards compatibility is great, and ideally no data would ever be lost to bitrot, but backwards compatibility always has a cost. I'm not unilaterally willing to pay that cost.
Is it really so difficult to just not break a feature that was present in the last version of the software?
At worst (like in the case of iWork 13 which probably is completely new code), you get one programmer to spend a few days writing a converter which reuses most of the old code.
Software is hard. I think it's pragmatic for software vendors to have a strong, transparent philosophy about the trade-offs so that consumers can make the right choice. As the grandparent points out, Microsoft values backwards compatibility. If you value that too, buy Microsoft.