I heard the same thing as jlandes, about 8 years ago (seriously, with outlook 98 or 2000). I kinda thought they addressed that and fixed it though. Maybe not.
I think I understand your question though, Jeff.
You had a email come in with 1300 addresses in the to box, and your email client decided to display the entire list, and in order to see the email, you would have to open the email. Annoying.
Outlook restricts the size of the to box to 4 lines in the previewer, and 4 lines in the actual email. If the number of addresses is great then that, it does a scroller, but still only 4 lines viewable. The message is still easily viewable regardless of the number of addresses in the "to" box. While many here might not like Outlook, the handling of this issue seems very eligant.
That said, users might want to be able to see all these users for a sad form of proof they sent emails to all those people (collaboration). Maybe display a few, but if the # gets to large dump them in a text attachment or do a scroller or something... or possible put a large to list at the bottom instead of at the top.