No shouldn't be because of lack of backups...1 hours is good..or could do 15 minutes if they are very big logs to keep them down a bit when backing them up. Ask the sharepoint guys if they are doing search indexes and if they are on MOSS which i think is the latest version of sharepoint.

Also ask them if they are doing rebuilds on the app side or setting up new search indexs on the apps.

Thread i found looks interesting.

http://sqlcat.com/technicalnotes/archive/2008/12/09/diagnosing-transaction-log-performance-issues-and-limits-of-the-log-manager.aspx