Size_t on x86 is uint,on x64 is ulong,it's a good thing?

[FrankLike via Digitalmars-d]

 Size_t  on x86 is uint,on x64 is ulong,it's a good thing?
  I don't think is ok.
  it  creates many convert  thing,such as length is ulong ,must 
cast to int or cast to uint. It will be waste of time ,I think.