Not at all. The old "x" postfix was used in Solaris 7 - Solaris 9 to indicate a 64 bit package.
The non-x package, in this case SUNWscpu would be a 32 bit package, and SUNWscpux would be a 64 bit package.
Starting from Solaris 10, the SPARC version is only 64 bit, so all the 32 bit packages was removed, and with them the 'x' postfix.
SUNWscpu - 32 bit in Solaris 7 - Solaris 9, but 64 bit in Solaris 10+.
SUNWscpux - 64 bit in Solaris 7 - Solaris 9.
So in short its gone since the naming convention is no longer necessary.