Yes, you're right! In practice, though, we're finding that many useful customizations can fit into that framework. For example, the Expedia demo in the paper shows a "1 row table" to represent an input form. It's worth thinking about how many different things people use spreadsheets for...

I think another useful analogy for thinking about abstract data representations is text streams in UNIX. It turns out many types of data can be represented as newline-delimited text, which enables you to use a suite of generic tools with that data. Inevitably, some data doesn't fit into that format, but it's perhaps surprising how much does.