L4_Word_t vs. void*

I notice that the L4 headers use L4_Word_t (and never void*) to refer to
addresses.  Is there a reason why L4_Word_t is a better choice?  Should
I avoid using void* in my own L4 programs?

I imagine there are 32/64 bit issues here (and perhaps even 32-on-64)
that I don't fully understand.  Can someone enlighten me?

Thanks,
Josh