One of the problem is that unless you crash-test your flash cards, you will
never know if their wear-leveling algorithm is fine or not. And I suspect
that nowadays, due to very large consumer demand, flash cards price drop
at the cost of reliability. I think that most of those not flagged
"industrial-grade" do absolutely zero wear-leveling, because they are sold
to people using them in digital cameras, and they will never kill their
device with such a usage.
I'm certainly not the only one with this requirement. A lot of embedded
motherboards come with IDE compactflash connectors. This is very convenient,
but if you need to keep informations between reboots, you have to write to
the device anyway. If you need to do that very often, either you pray for
the device to be very reliable, or you take all the chances on your side
by adding your own wear-leveling "just in case".