If Blockland had voice chat, it would suffer the same fate as Halo 3.
Lots of young kids screaming their heads off every time they died (considering you were in a T/DM).
"DAMMIT YOU STUPID MOTHER-loving rooster SUCKER I HATE YOUR GUTS YOU friend"
Of course it would be nice for people who were just building, but I think using Skype/Ventilo/some other thing would be better.