[boost] [typeof][implementation]why not use decltype or conditional expr?

Why couldn't the BOOST_TYPEOF macro be defined to simply use the new keyword, decltype, if it's available? I assume the macro, BOOST_HAS_DECLTYPE, indicates whether it is available. And if decltype not available, why couldn't it use the conditional expression method described here: http://www.artima.com/cppsource/foreach2.html I would think that would be simpler and more portable. -regards Larry