New spreadsheets should only have a single sheet
The normal thing is to only want one sheet. If I want multiple sheets I would normally want more than 3. It is easier to add a new sheet than delete one you don't want. Also many of the formats you can save a workbook in don't support multiple sheets. As such I think it would be more user friendly to only have the one tab to start with.
Excel versions starting with either 2007 or 2010 (I forget exactly) now have only one sheet by default, as we came to the same conclusion that you did.
Also, as Kenneth mentions, you can change this value here: File → Options → General → When creating new workbooks → Include this many sheets.
Hope that helps,
Kenneth Barber commented
Change the number of sheets that new workbooks start with by going here: File → Options → General → When creating new workbooks → Include this many sheets.
If Excel were to default this setting to 1 sheet, I can easily see people that are new to Excel try to cram everything into 1 sheet, since it's not obvious that you can add a new sheet based on just 1 sheet tab. The default would have to be at least 2 to establish the fact that workbooks can have multiple sheets.