Simply put, members of the business community are lining up behind Mr. Emanuel because they think he most shares Mr. Daley's strongest traits. They see the one-time investment banker as an economic centrist who will play hardball with municipal unions, someone who knows the labyrinth of Washington and can exploit his worldwide reputation to further Chicago's global ambitions.
This is interesting. If you wanted someone with the most direct Daley experience, Gery Chico would be the best bet, a loyalist who's bucked Daley a little bit of late. If that porridge is too Daley, there's Miguel Del Valle, who's sort of Preckwinkleish in having progressive bona fides but who isn't an outsider (obviously, he's city clerk). But Emanuel has the perception of being like Daley but perhaps without the baggage of actually being connected to the city during its unpopular financial crisis.
It's curious. This could be a fascinating race if it doesn't turn into a fait accompli based on Rahm's Clout 2.0—the promise of less tangible but more extensive power (national... multinational, even!) instead of the assurance of civic leverage.
[As always, the Chicago Mayoral Scorecard is your best shot for who's in at a glance.]