"sponsoring employer" can be changed any time by the visa holder applying for 'H1 transfer' with USCIS. Your wikipedia quote is correct but the impact is just that you can't have multiple jobs without multiple H1Bs (one person can have up to 4). Since you can change the sponsoring employer any time, you can change jobs any time.
Since my parent post got voted down, I should probably note that I am on H1B and I've done this myself.