Neither Blockland nor Roblox is an MMORPG, or an MMO for that matter.
RPG is obvious, as there is no item collecting or money making except in mods.
MMO is a little harder to explain, but I''l do my best.
A true MMO has multiple servers that all have an exact same copy of the original game world on it, like in WoW or Lego Universe.
Blockland has multiple different servers all hosted on different maps with different amounts of bricks, players, and different builds.
Same goes for Roblox.