Chicken and Egg though.
Why would they commit anything when Perth Airport is not configured the way they feel they need it for the services to be profitable? They are trying to avoid the issues associated with separate terminals that currently exist. The carrot of these services and their potential economic benefit to the State is being dangled so they don't have to wear the cost and thus, the risk, if the services don't work as planned.
Sydney and Brisbane are inconvenient for domestic to international connecting passengers because of separate terminals. Now in Perth, they have a unique opportunity to introduce a common terminal for all of their services and remove this inconvenience, until a common facility is completed at the current international site.
If a combined terminal facility is the deal breaker, they aren't going to announce services unless they get what they're asking for.
You don't walk into a Car dealership and say "I am definitely, no matter what, going to buy that car and I am not going anywhere else... Now... whats your best deal?". Well, if you do, you're a fool.
If they were to say that these services are definitely going ahead no matter what, they'll certainly get nothing, because there is nothing for the other stakeholders to lose. BY the same token, this could be a bit of a ruse to get Brisbane or Melbourne Airports to offer better arrangements for the direct Dallas services that both are pushing for. Either way, Qantas potentially gets a better deal out of it somewhere(not to mention some nice free publicity). Perhaps QF also gets a move to a common user facility on the International side in a shorter time frame than currently promised, as GT and the other Media in Perth go to town on the State Government and Perth Airport management for 'costing' Perth these services.