Michael Pahl's Source Theory

Michael Pahl (weblog: the stuff of earth) has two relevant blog posts on his solution to the synoptic problem (his preamble and proposal). Unfortunately he doesn't specify why he sees Luke's use of Matthew more plausible than an oral-Q source/sources which is intriguing given his emphasis on oral traditions. Was Luke running short on oral sources for the Mt-Lk-double-tradition(s) and had to turn to the gospel of Matthew for it/them?