I read a nice article titled "Why Open Software Matters." The quote below sums it up well.

So, now you've got ten years worth of essays, articles, assignments, photos, music, and other memorabilia saved as a file that no-one else knows for certain how to open, or is not legally allowed to. I'll say again, this type of restriction is not illegal. No company is required to release how their programs work, and they are most certainly not required to let anybody go around imitating them willy nilly. This use of closed standards results in what is known in the industry as "Vendor Lock-In", and is a well known strategy of large software houses. You must keep buying products from the same company if you want to keep up to date software, and you're up the creek if they decide to no longer support a feature you really need, or they refuse to grant license to other companies to work with the types of files you are using.

-Chris