I think TK also does not have an economics degree. Otherwise, he might have come to the conclusion that Exp2 didn't sell as well because maybe people weren't really capable of spending money at the time?
Also, frankly, Exp2 was underwhelming besides the ME, and if you don't care for the ME, you bought it for nothing. The campaign customizer as DLC was a good idea, because if people don't want it they don't have to pay for it (although I think that SHOULD be standard because it enhances the otherwise limited campaign options, and when you have no MP and ONLY single missions and campaigns, you really need either the ME or the CC in the game if not both). However, Exp2 was pretty much "some obscure Euro jets" other than that. To non-Europeans its appeal must have been small. At least Exp 1 had the P-51 and covered the relatively famous late 40s war in Israel.
Finally, while I bought and enjoy them all, I think the route he took with SF2 was a mistake. Redoing SFP1, WOE, WOV, and WOI should not have been done. SF2:NA should've been the first SF2 title. People are STILL flying SFP1 and its brethren, and while SF2 is better it wasn't NECESSARY. He could've switched to the SF2 engine with 1 new flyable plane per title/expansion, kept the ability to use SFP1 mods (as most of the early SF2 mods were just ports), or just dumped the mods and put MP in as he said he might in the past (his notion that mods and MP are mutually exclusive I don't agree with, but there you go). Let's face it, SF2 as it is today with just a flyable F-14 but MP would sell great. The MP would have to be more than we had in SFP1 (random missions only) because it was too little, the ability to do campaigns or at least to do scripted missions in addition is needed. Don't dump the random, though, because in say DCS or RoF I constantly have the problem of lack of MP missions to fly and there's no options for campaigns or randomized missions there. I would love an SFP1-style random MP mission ability for both of those.
Also, while it must be nice to get almost 100% of your sale price for yourself, I really think TK should look to Steam. Raise the prices if needed, but Steam has exposure. Just showing up when people search for "flight" or "sim" in Steam would be instant ads. There's also Impulse/Gamespot, Direct2Drive, and others. What's TK's ad method now? Word of mouth from existing customers? People stumbling across his FB page? Random Google searches? Inefficient.