j0h, you are describing exactly what families do and what they're for. Why wouldn't you put "Left_block", "Right_block", "Top_block" and "Bottom_block" in a family "Blocks", and use the event
+ "Blocks" on layer 7
--> Set X to ...
You may argue you'd have to put every Sprite in your game in to one family, but this is necessary. Any large, complex game will have sprites for completely different purposes, ranging from the player, enemies, interface, terrain and effects. Applying events indiscriminately to all of them would not be useful, and you would want to specify exactly which, by using a family.
If there WAS an 'All sprites' type family automatically built in, you'd probably run in to some serious problems quickly. If you code 100 events using 'All sprites', then you add another Sprite you don't want to be affected by all these events, you have to add a family to all the objects you want to affect, then edit 100 events! It might be boring going through adding a family to a lot of objects (perhaps a Family Manager dialog could be added to make this process quicker, eg. mass-selecting objects and adding them all to a family in one go), but I think it's the best solution, because it gives you the option of not having a Sprite affected by those events.