Minecraft itself perhaps does not care, but a 32-bit JVM process will have a 4Gb heap tops (3Gb on Windows) that will make the playing experience either unpleas

Minecraft itself perhaps does not care, but a 32-bit JVM process will have a 4Gb heap tops (3Gb on Windows) that will make the playing experience either unpleasant (i.e. constant garbage collection running in parallel and stopping Minecraft worlds) or will plainly fail as Minecraft creates a very large number of objects, esp. in large worlds, that won't fit into the JVM heap – each thing in Minecraft is a Java object.