As I recall the accepted upper limits for a business to be classified as small, are actually rather high, in terms of gross receipts, profits, staffing levels, and payrolls. And that was probably done to give some wealthy campaign contributors access to small business tax breaks, interest free government loans, etc.
Some companies with a national presence, that most Americans would immediately recognize from TV or print advertisements, are actually "small businesses".
I can't immediately cite any examples but I'll do a search and edit this post.
Anyway my point is that these very large small businesses are the ones which would be affected by an expiration of the bush tax cuts and that actual small businesses would never notice it.
On edit: see attached article from Guardian Online - Bechtel Corp. is a "small business".
http://www.guardian.co.uk/commentisfree/michaeltomasky/2010/sep/21/obama-administration-congress-small-businesses-like-bechtel