I actually believe Webb is more marketable than Greene (domestically, not internationally).
There is always a 'World's Fastest Human', but Webb's story is unique. Did ESPN ever break out of its normal programming to telecast a Greene race? Even the announcers stated the USATF crowd was there to see Webb over Marion. (Although that was last year, when Webb was red-hot). Most people I talked to knew of Webb, but far less knew of Greene, even though he had accomplished so much more.
If Webb can have the kind of 2003 that we thought he would have in 2002, then he will capture everyone again, (but not quite like before). But even right now, if he were in a race, the interest would snowball tremendously.