i don't know if Musicology will be released as a retail single but it sure makes a difference on the charts

here is todays airplay top 10

1 1 BRITNEY SPEARS Toxic 8680 8699 -19 76.728
4 2 USHER Yeah (f/Ludacris & L... 8237 7754 483 75.827
2 3 EVANESCENCE My Immortal 8021 7945 76 72.928
5 4 MAROON 5 This Love 7522 6802 720 67.425
3 5 JESSICA SIMPSON With You 7322 7803 -481 62.734
6 6 OUTKAST The Way You Move 5501 6061 -560 43.070
9 7 CHINGY One Call Away 5488 4887 601 45.322
7 8 LINKIN PARK Numb 5248 5632 -384 49.048
8 9 NICKELBACK Someday 4643 4994 -351 37.245
11 10 HILARY DUFF Come Clean

now look at today's regular billboard top 10

1 1 13 Yeah!, Usher Featuring Lil Jon & Ludacris <----retail single
2 2 10 One Call Away, Chingy Featuring J. Weav
3 3 12 Tipsy, J-Kwon <----retail single
4 - 1
Solitaire, Clay Aiken <--- retail single
5 4 16 Hotel, Cassidy Featuring R. Kelly <--- retail single
6 7 11 Dirt Off Your Shoulder, Jay-Z <---retail single
7 6 14 Splash Waterfalls, Ludacris <--retail single
8 10 13 My Immortal, Evanescence
9 11 7 I Don't Wanna Know, Mario Winans Featuring Enya & P. Diddy
10 12 8 This Love, Maroon5

also 19 of the top 30 billboard hits this week are out as a retail single