This is a pointless thread. Ultimately who cares? Progressive talk is a marketing label, and listening to the myriad of hosts on AAR and other libtalk shows, they all call themselves progressive and liberal.
There is no mystery about why these two terms have been bandied about. Conservatives spent millions demonizing the word "liberal" since Reagan came to power. The mistake liberals made was not being willing to fight back, assuming it wasn't that important to waste time and energy on labels. And they were wrong to do so, and in this country, not fighting fire with more fire is considered "weak."
As a liberal, I can say I have used both phrases and I consider them essentially interchangeable. Progressive doesn't carry the "baggage" that liberal now does, and because one will have to spend a lot of time and effort trying to undue the demonization of the word before people get past it, why not just change the word? This is hardly something new. People change strategies and words all the time especially in marketing.
We have a lot of Republicans running for office this term that never mention they are "conservative" or Republican in their ad pieces at all, because those polled negatively during this election cycle.
I'd say being called "pro-Bush" in this election cycle is a death wish in a lot of areas, so they just don't do it.
I am surprised if anyone really didn't know all this already before they started a thread about it.