I can speak to Veritas NetBackup.

You are correct that a tape is created for each full and incremental, but
there is a feature in NetBackup that allows you to multiplex the server
saves to a single tape up to a limit you specify.  This really great until
you try to duplicate the tapes for offsite storage.  The duplications tape
literally exponentially longer as the number of files gets larger.  We found
it quicker to run the full backup twice than to duplicate the tapes.  The
backup involved ran for about 20 hours on a full to get the two copies.
This was using Magstar tape and Shark disk, big file system on a high end
UNIX SGI machine.

The real issue is NetBackup supports the original and a duplicate only.  It
supports 9 retention periods only.  It does not have a deleted file policy,
so once the tapes expire the data is gone.  It is tape expiration oriented
instead of object.  It has a tape catalog and what files are on the tapes.
When you do an incremental restore there is no directory structure rebuild,
meaning that files that have been deleted are restored, so the concept of
put the system at point in time does not exist.  This can play havoc with
applications using touch files to signal application progressing.

You talk about more tapes, but more tapes also means more tape drives to
process.  There is no disk pool concept in NetBackup.  It is written
directly to tape, period.  This is where TSM eats NetBackups Breakfast,
Lunch, Dinner and Midnight Snack.  We took a 12 Magstar drive NetBackup
windows environment using about 180K of NT hardware and migrated it to TSM
using 6 drives and a AIX P660.  Nothing else changed except it freed up 6
high end NT servers.  Instead of running a few of our 108 servers each night
on full backups and round robin throughout the week, no C: drive backups, no
point in time restore capability, duplicates often late getting offsite,
only 2 weeks of recover, we now have a primary, onsite copy, offsite copy
and sit around joking about the days of the NetBackup debacle we extracated.
The company is about to adopt a daily offsite strategy.  Thank you TSM for
making it a possibility.

Plain and Simple.  NetBackup is extremely expensive to run.  The maintenance
on the software is much higher than TSM, it costs more than TSM, it uses at
least twice as much hardware as TSM, has horrible support, and just plain
does not scale.