I have finally found a fix for the problem on the BB Pearl (8100) that there is no "Keep Appointments" option, which means that you cannot prevent old calendar items from being deleted.
This has been recognized by the BB people as a problem. In their horrible jargon "This is a previously reported issue that has been escalated internally to our development team. No resolution time frame is currently available.
" and in English "Yup, we screwed up, and although we keep getting bugged about it, we have more important things on our minds, as this phone is already out of date." To be fair, despite the BS they have posted a fix on the blackberry.com site. (So why can't they learn to speak proper like wot I do?)
Go to the Knowledge Base Article KB14214
, download the file attached there and install as instructed - it worked for me! All my old calendar items are kept on the device and do not get removed from Outlook on synchronization.