It wasn't the only method to overflow though. After Extended Unit Deaths were patched, I tried extended alliance status, which worked, and caused yet another patch. Since then, extended switch states and other methods I've tried testing have resulted in failure.
What people don't understand is that even with EUD conditions, you can still do a lot, and Deaths isn't the only condition that can be used for overflow memory detection.
Command, Accumulate, Kill, Command the Most/Least, Most/Least Kills, and Score can all be used. Since the player number is four bytes, you can pretty much read any memory after player 1's minerals at 0x0057F0D0.
Using a Most/Least overflow, you could easily come up with Most/Least Deaths.
Using an accumulate overflow, you can reach a bit lower in memory, before the Deaths Table at 0x0058A344, to access supply, saved groups, and some other things.
I've done a lot of memory mapping, you can view my work here: http://code.google.com/p/bwapi/wiki/changes116
I just want to say that not all the resources for new techniques have been exhausted, and there will definitely be more on the way.
Some untested things remain, like extended locations(conditions and actions), and extended string referencing(actions). Some overflow writing still remains, like preplaced extended units and extended players.
Starcraft mapping is about using your imagination to creatively come up with new concepts. It's not recommended that you use an overflow in your map because of compatibility issues, but it's certainly an option you should consider in the creation of a map.
Overflows don't just exist in triggers and preplaced units though. You probably didn't know that Set Doodad State, Disabled Sprite-Units, and player colours are overflows themselves. Set Doodad State and Disabled Sprite-Units read overflow IScript entries. Disabled Sprite-Units reads the in-construction animation, and Set Doodad state has its own entries. Colours over index 11 read as an overflow, and the Flag unit is one result of crashing due to an invalid portrait(overflow). If you can avoid the flag's talking portrait, you can overflow and display even the beta portrait.
Another technique that uses an overflow(and I'm surprised nobody has found a way to use it practically), is the hallucinated powerup glitch, involving a hallucinated powerup running out of energy in a worker's hold so that when a new unit is created, it will replace the powerup that was in the worker's hold, teleporting the new unit to the worker's destination on its destruction, and applying the powerup property to the unit so that it can be picked up.