Consolidated audience figures - including recorded viewing, which accounted for 40% - showed Dexter season two opened to 734,000 across three timeslots on the channel at the beginning of the month.
"This is obviously a good result from a great campaign but these sorts of figures are not unusual for us anymore," Thorp said in a statement hailing the performance.
"I am fed up with hearing 'hidden gem' and 'all the good shows are on a little known channel FX'. We are reaching 5m people a month, we are playing with the big boys now."
Thorp also defended the audience for the first episode of The Wire's fifth and final season on Monday night, which overnight figures put at 38,000.
"Fifty-thousand viewers [sic] is not a bad result for such a piece and that figure may well double with consolidated data and playback," he said.
"We don't support shows like The Wire for ratings alone, we have other more populist shows for that. We back The Wire, Carnivale, The Corner and Generation Kill because they deserve to be broadcast because of their quality alone.
"It is telling that PSBs are not prepared to take a risk on them, preferring shows such as (BBC Three's) Snog Marry Avoid, a fact that makes me think we should be applying for public funding!"
The comments come as the government reviews policy on public service broadcast funding, while the BBC Trust has reportedly asked for BBC Three to focus on more wholesome programming. Sky, a News Corp stablemate of Fox, believes much of its content should be considered PSB, despite requiring a subscription.
Thorp's comments about the PSBs appear somewhat at odds with Sky's view that the BBC should not be bidding for premium films and US television series, however.