confusion in base regarding [option os.arch] and ${os.arch}

[Jeremy Lavergne]

reading through base, it looks like os.arch is set to something based   on
its original value, while that original value is actually used as  
os_platform (and os.platform). if this is the case, those changes were  
never ported into port[un]archive.tcl. i don't understand how to  
reference platform correctly from there, as it seems that the values   are
different when they're pulled from [option os.arch] versus $
{os.arch}

any care to shed light on this for a newbie tcl'er?

what i essentially want to do is change archive.fulldestpath from   [file
join ${archive.destpath} [option os.platform] [option os.arch]]   to [file
join ${archive.destpath} [option os.platform] ${os.arch}]   where os.arch
is x86_64 or what have you, instead of option os.arch's   i386

if i understood the transforms in portmain.tcl then that's what should  
be done here. incidentally, after this one change we can actually do  
binary distribution via archivemode