Sorry Stranger.. that isn't true...

The reason some (many) of us use XP is because one CAN book complex multi-airline itineraries... which is what I imagine jcamp028 has done.. (sure sounds like it!)

Such itineraries are ONLY bookable on such a site - or as you mention through a travel agent at extra cost... I use both methods.. and because I lock down my plans before booking I have had no dramas with XP booked trips...

Seems the majority of XP complaints relate to trying to make changes..

On what airline site could I book a trip that used airlines in the following order... CX,CA,OZ,SQ and AC?

Yes, there are limitations to 3rd party bookings... but one can work within those restrictions to do things that are difficult to achieve any other way....