Unfortunately this always seems to happen each time there has been an upgrade. I suspect they want you to pay that additional 25 bucks for the use you have had out of the previous version.
Be glad that you are in the US. Here in Europe ( and I think Oz) the upgrades are priced locally. So here in the UK we pay £71 gbp, the equivalent of $115 for the CS5.5 to 6 upgrade.
I'm in the same situation and feel the same way. I upgraded (?) from 3.0 to 5.5 in January as soon as I learned that there was a 5.5. I had some new projects coming up and wanted to use the latest and greatest version. Well, 5.5 was not an upgrade and I don't see how anybody could call it that! I spent more time with tech support and on this forum trying to work out problems than I did using the program. I finally gave up on 5.5 and went back to using 3.0. I did not try to do a return or get a refund because everyone kept saying that CS6 was on it's way and all of the functionality would be back. I assumed that with all of the complaints and hassles that 5.5 brought on, Adobe would probably offer a free or nearly free replacement with CS6. Now I see, as does the original poster here, that it's actually going to cost me an extra $25 because I did buy 5.5.
I like ryclark's comment, " I suspect they want you to pay that additional 25 bucks for the use you have had out of the previous version." but I feel that they should PAY ME because all of the time I wasted on this fiasco cost me way more than $25! I'm really disappointed and upset with Adobe for this!
What still rankles here in the UK is that the upgrade from, say, 3.0 to 6 costs $50 more than it does in the States. This then means that we pay tax (20%) on top of this extra, so we lose out twice.
Corporate users will bypass all this, of course, with special deals, reclaim of tax and so on, so it's the small, non-commercial, home user who loses out.
Or even the small, commercial user with only a couple of seats.
While we're talking rankles to do with international pricing, the upgrade cost down here in Australia is only a couple of dollars short of double the US cost. Ten percent of that is tax (which, under Aus law, wouldn't be payable if I could order and download from the USA); the rest is just plain price gouging since the Aus dollar is stronger than the American one these days.
In his announcement about CS6, one of the developers (I think it was Colin) said that they were aware of the customer annoyance at these huge price differentials and suggested that every phone call to the local customer service is noted by the powers that be. I strongly suggest that all of us outside the USA make a point of phoning in our complaints rather than just posting them here.