Legos are manufactured with surprisingly fine tolerances. You might be able to do it with the Replicator 2, I don't know.

They've also got a lot of 90 degree overhangs, which FDM machines don't like. (It's essentially a hot glue gun in a gantry. The plastic doesn't freeze instantly when it leaves the nozzle, it stays molten for quite some time. If you print over thin air, it'll droop.)

And if you could print it, the bottom layers might delaminate and break off every time you detached it from another brick.

As for a flowerpot, no way. PLA's made from corn. Keep it warm, wet and in contact with soil, and it'll turn into compost within a month.