I've heard this before.. but never quite understood the logic.
/home will always be on a partition with a given probability of failure.
Whether or not /var is on a separate partition does not seem like it would much affect probability of the fs metadata for /home getting corrupted.
I suppose /var may get written to more frequently (and thus increasing the chance of messing up the fs metadata), but on a desktop system, I would think the difference in the rate between which /home and /var is written is not that great.
And I haven't ever had trouble upgrading a system with a single partition (another common reason given).. installing a brand-new OS, yes.. upgrading no.