Michael, it’s not make that supports for DESTDIR – it’s the Makefiles that do it, usually as one of the many features picked up from automake. Half the problem SCons has with this is that there’s no similarly pervasive tool set to at least set standards (even people who don’t use automake often emulate the features that people actually use) and the focus has mostly been on pure make functionality so there’s really nothing there for installation and packaging. This has resulted in projects using SCons each coming up with their own approach to these things – which can boil down to no approach at all.
The situation for SCons ought to be improved fairly soon thanks to a pair Summer of Code projects from this year and last year which will together give SCons automake-style functionality – hopefully once they’re merged people will start using them when they distribute their software. In the meantime you could always ask upstream to implement DESTDIR support.