Correct, collaboration is much better (realtime editing/chat/cloud storage and sharing).

Admittedly, Excel has a smoother editing experience (which is the real issue here) and is probably better suited for more resource heavy tasks, but Google Spreadsheets excels [intentional] in the following areas:

API -- http://code.google.com/apis/spreadsheets/

Scripts/Templates -- http://code.google.com/googleapps/appsscript/

Forms -- http://docs.google.com/support/bin/answer.py?hl=en&answe...

External data functions -- http://docs.google.com/support/bin/answer.py?hl=en&answe...

Revision History --

Some of this might be achievable in Excel, but it's not integrated as well and requires much more wrangling (e.g. VB scripts).