I'd be surprised if that generous UA policy remains in place 2 years from now. The trend is to charge for standby.
Not true. On UA, you get charged $75 unless you have 1P status or higher:
http://www.united.com/page/article/1,,52142,00.html
Note that this fee applies even if you're traveling on the highest fare (Y/B).
On WN, you can standby but you have to pay a fare difference. If you're already on the highest fare (Anytime/Business Select), and the same fare ticket is available on the earlier flight, there is no charge.