"rpm -qi package" gives no indication of the architecture for which the installed package was built. To see this, try: rpm -qi glibc and examine the output. Nowhere will you be able to see whether the installed package was *.i386.rpm or *.i686.rpm, for example. Granted, you can find this information via: rpm -q --queryformat='%{ARCH}+AFw-n' glibc but it ought to be shown by default in the general info listing.
Query the arch tag, or, if you wish, edit /usr/lib/rpm/rpmpopt-* to add a query for the arch tag to the popt alias that actually implements --info. I'm unwilling to make the change in the "default" configuration because a) rpm -qi already exists with well defined output b) most users don't need to see the arch tag because ... c) ... most packages do not benefit in any material (i.e. no significant performance gain) way from changing arch because ... d) ... what is really desired is to know the optflags used to compile the package. Try looking for RPMTAG_OPTFLAGS rather than RPMTAG_ARCH.