But, why re-downloading every hour?

Does merely having the spreadsheet passively open in a browser trigger that, or was some other process re-loading the spreadsheet every hour? (If the former, I wouldn't be as forgiving of Google. I understand the desire not to cache possibly-private data, but proper URL design and conditional GETs should be able to prevent the entire download on an automatic hourly schedule. And even if the latter – the author had chosen to reload the spreadsheet each hour – I'd want Google's design to allow browser-side caching to work for such embedded and/or generated images.)