They aren't alone in this of course, the Yahoo Publisher Network also has a hundred dollar minimum pay out, although other programmes such as Amazon Associates or TradeDoubler have a lower thresholds, at least for direct deposits.
However none of these other programmes do targeted text adverts. If you want targeted text adverts, and you live outside the continental United States, then your only option for now is Google's AdSense. I'd guess that's what they'd call a market opportunity...
Update: It looks like Nicholas Carr has been reading the AdSense terms & conditions again, and has posted a follow-up article to his discussion of the Google float. He's concerned about section 6 (viii) which prohibits the publisher from;
(viii) act in any way that violates any Program Policies posted on the Google Web Site, as may be revised from time to time, or any other agreement between You and Google (including without limitation the Google AdWords program terms), or engage in any action or practice that reflects poorly on Google or otherwise disparages or devalues Google's reputation or goodwill. You acknowledge that any attempted participation or violation of any of the foregoing is a material breach of this Agreement and that we may pursue any and all applicable legal and equitable remedies against You, including an immediate suspension of Your account or termination of this Agreement, and the pursuit of all available civil or criminal remedies. - Google AdSense terms & conditionsNow I'm not a lawyer, I'm not even an American citizen so my grasp of US law is some what vague, but I'm not really sure I agree with Nick's interpretation. He argues that is is basically a gag order on publishers, denying them the right to criticise Google in press. To me it doesn't read that way, but I guess it really hinges on what the word "action" means in US law? Anyone?