Fully expected.
If it's bothering you, you could do some analysis of what indexes are getting rebuilt the most and reduce their fill factors so that they fragment less and hence get rebuilt less.
Switching to bulk-logged recovery will not help. In bulk logged recovery index rebuild are minimally logged and hence the log file itself does not need to be as large, but the log backups will be just as large as in full recovery.
Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability