There's a straightforward way to resolve this once and for all: if Thesis is indeed GPL, then it doesn't matter what license Pearson uses - anyone can legally copy/distribute/modify/fork/sell Thesis publicly right now, even if Pearson continues to opine that the code is distributed under a different licence. GPL is GPL.

Pearson will most likely sue the first person who actually does this (and refuses the Cease-and-Desist that precedes the suit). The courts will then determine whether or not Thesis is indeed GPL, or whether the distribution was in violation of Pearson's intellectual property rights.

Until someone actually does this, the debate will continue - there's enough ambiguity that the issue won't be resolved until ruled upon by the courts. I really doubt Matt/Automattic will push the issue - there's a lot to lose and almost nothing to gain. (Matt said in a previous thread he thinks Thesis' code is "junk" and doesn't want it in core.)

Until Thesis is publicly distributed and legally challenged, the status quo will continue: Thesis will effectively be private code, and Pearson's position will prevail.