/dev/sdb and /dev/sdb1 are devices, not mount points, although they can themselves be mounted.
/dev/sdb is the second detected SCSI drive, /dev/sdb1 is the first partition on the second detected SCSI drive (/dev/sdb2 would be the second partition, and so on).
The reason you can't mount /dev/sdb is that it is not a partition - it is your entire drive, partition table and all.
You probably have some sort of auto-mounter enabled, which would explain why you can see files when you click on /dev/sdb1 without having to type:
mount /dev/sdb1 /some/mount/point
in a terminal. According to your mtab, the mount point chosen by your auto-mounter is /media/sdb1, which would be a directory and not a device.