As Wilhelm's analysis notes, SOE is getting out of the business of allowing Station Cash to pay for anything that was previously worth paying for under the old subscription model - no expansions or other content and no subscription fees. They are fully entitled to do this. Indeed, it's puzzling that they are just now noticing that Station Cash sales were reducing the cost of their product - I'm pretty sure that February 2010's Sentinel's Fate expansion was available for Station Cash (after the one-week retail exclusive window). As Bhagpuss notes, they even managed to announce it properly and in advance. (On the downside, they just learned that lesson the hard way, but at least they learned it rather than repeat it.)
The last time I took part in a triple Station Cash sale, sometime around April, I was on the fence about whether to purchase $15 or $20 worth of credit. I elected the latter, rather than fund the stuff I wanted to purchase out of my existing balance - I figured that I would likely use the extra SC to pay for content or game time in either EQ2 or DCUO.
Having learned that this month is my last chance to spend the SC on content, I elected to call the $5 a relatively cheap reminder of what happens when you purchase more virtual currency than you have immediate plans to spend. I cut my losses and grabbed three DCUO DLC packs that I may not ever use, rather than continue to hold a SC balance that increasingly cannot be used to buy anything that I want.
As Spinks kindly noticed, just last week I was rambling about whether the DLC model for MMO's is actually sustainable. I'll be the first to concede that paying SOE $20 for all of the paid content they added to both of the two SOE games I played over the course of a year certainly does not fall into the sustainable category. That said, I'd have more sympathy for their desire to receive an honest day's pay for an honest day's work if it weren't for their own self-inflicted and self-described "aggressive" marketing practices.
The problem is that the cost of Station Cash item can vary by more than six-fold if you stack a triple station cash promotion with a 50% off sale and a Walmart-exclusive point card bonus. Players did not create that situation, and you don't see SOE similarly crying about the need to "protect the revenue they need to offset costs" of the mounts and vanity items they will continue to offer in the SC store for nominal prices that exceed $10 per item per character.
To preserve this "aggressive" regime, they are cutting off the ability to pay with store-bought cards. To my knowledge, EQ2's most recent expansion was not offered in retail stores (presumably due to the retail cut), so SC was one of the last avenues available for those who don't want to provide a company that got hacked last year with their credit cards. They're also removing a mechanism for price discrimination by players like myself who don't play enough to justify $220 annually in expansion and subscription fees but who would otherwise be happy to support the product. Given how thin this year's content is, I'll be hard pressed to justify yet another $40 expansion box - potentially the third in 20 months - this fall if I have to pay full price.
P.S. In a mostly unrelated story, Bioware's single player DLC division has some commentary on how successful the model is - the comments have a distinct feel that people who don't like it are out of luck because every single player game will be diverting content from the release game to paid DLC within five years.