I too have been buying one way tickets when I have companions to worry about, BUT in the case you need to change your plans now the problem is you have twice the change fees to deal with 2 fees @ $200 each x 2 pax. When booking a RT you can change both the outbound and inbound by only paying one change fee, but no so if you book two one ways.

Normally I take this risk but it still irks me that UA would be able to extract $400 per ticket from me if I have to make changes; in many cases this exceeds the amount of the ticket so one would just have to "throw it away".