My only conclusion is that a property slump would cause such massive damage to the ISE that these guys have now decided that they could lose more than they gain by trumpeting stocks as a better investment than property....
I think you're right about that. Out of the twenty companies selected for the ISEQ 20 index over half are focused on property related businesses. A cursory glance shows a lot of banks, construction companies and property/land holding companies.
If the property market tanks then it would not be surprising if the ISE saw a huge amount wiped off it.