Great questions and you are right to be thinking about Static Control and the related caselaw. It's hard to know exactly what would happen if this one were to get litigated -- both because this is a relatively new area of the law (figuring out when a DMCA copyright
case is so removed from the purposes of the copyright system that a possible technical violation of the DMCA ought to nonetheless be ignored) and because some of the analysis would turn on exactly what the software says and does, let alone what (if anything) the relevant patents
might cover. Note that they also hand-waive in this letter about other possible legal theories, though some of them (like the trade secret
point) sound ridiculous on these facts.
The question for you, though, isn't just whether you are right, but whether you want to deal with the cost, uncertainty, and frustration of litigation related to these issues. The law firm that wrote you is a big, serious firm -- which means that the plaintiff here has already spent some real money to write you, and likely is willing to spend some real money to fight with you. Your intuition -- that they are in essence playing the same game that Lexmark tried to play with its print cartridges, or those garage door companies tried to play with their garage door openers -- sounds right to me, but it still could be a long, uncertain, annoying road between here and there.
All that said, your response is a great one. If the EFF were to get interested and write a letter back on your behalf, that might even the playing field a bit. No one in this situation wants the EFF to get interested; the EFF's track record here is too good. (Indeed, I'm going to send this information to one of my contacts at the EFF and see if that might help.) Another option for you would be to hire local counsel and fire back your own formal letter. I just hate to see you in the position of having to spend money to do that.
In short, then, on this quick summary of the facts, I think you are moving in the right direction -- the main issue here looks a lot like the cases you know about -- but now the question is whether this is a fight you want to, and can afford to, fight.
I hope the EFF steps up. This is spot-on for them.