Then you were extremely lucky :-) Maybe latest Bora is OK now but there were problems with this many times before with maemo 2.x and 1.x repositories and there may be problems in future again. Application manager upgrades just user packages. 'apt-get upgrade' gets also libraries and other system stuff which can break things and did that many times to many people before. Maemo repositories are/were meant mainly for scratchbox environment so there is no guarantee everything will work on the device. Also some upgrades may lead to stopping/restarting of critical services which may reboot tablet in the middle of upgrade and cause reboot loop.