You have google docs on the ipad, in fact on anything with an internet connection, which let you import/export office files.
If Microsoft decides to kill a feature available in Excel 2010, you still can use it.
Of course also the difference is that I paid for MS Office while I haven't paid a cent for Google Docs.
Individuals with that version installed can use it, but you can't get new licenses for more employees, and you won't be able to upgrade to get new features. You might also be wary of applying bugfix patches in case your key feature gets zapped. Also, user support for your feature will dry up eventually.