That's true, but I'm more worried about the media side. The media needs to hold up physically, and there needs to be continued availability of hardware that can read it. You can address both concerns by copying all your important stuff onto new, current media from time to time.
I'm less concerned about file formats. They are pure information. And when the time comes, chances are someone will have written the necessary conversion. When Captain Kirk is born on 22 March 2233, they will still be able to read PDFs.
To take an extreme example, taxcontrol advocates imaging your hard drive periodically, thereby simultaneously backing up your data and the applications to read it. Now, when Captain Kirk arrives, chances are there won't be any PCs capable of booting up your drive image. But there will almost certainly be virtual machine applications capable of simulating a PC on the computers of 2233. They'll just need to be able read the drive image off the physical media.
Perhaps by then the hardware will be up to the demands of MS-Vista. :-)