I believe one of two things may be happening with the cases you've heard of. (Though I'm not sure why you're saying you've heard more on this board, to my knowledge none of the mamas whose babies had TTTS have terminated, but I could be wrong)
First, depending on who your doctor is and how up to date they are, yes...this was often discussed as an option because up until fairly recently the survival rate for TTTS was not very good. Which is par for the course considering up until the laser surgery the only options one had for severe TTTS was to siphon the extra amniotic fluid (basically kind of a high volume amniocentisis with all the inherent risks) OR to have a hole poked through the diving membrane to 'even out' the fluid levels between the twins (which only increased the chance of limb/cord entanglement, and essentially turning things in to a mono-mono MZ pregnancy, with all those other risks).
Second, I hate to say it, but a lot of perinatologists engagne in CYA behavior. Frankly, for awhile when my primarily peri was out of town and I was seeing a different doctor every other day during the early stages of our TTTS diagnosis, EVERY SINGLE ONE brought up termination until I had a screaming fit and told them to write 'NO TERMINATION' on the file so that even someone who didn't bother to read the file would see it if they even glanced down, then later sobbed to my real OB about it--she got really pissed and went to bat for me and there was never another problem. I'm not proud of my behavior, but at the same time if they had a freaking clue and actually read my file they would have seen our wishes. Unfortunately every new peri had to reinvent the wheel until my episode, and they'll all want to cover their behinds. So you DO get a lot of pressure sometimes. Having someone tell you every other day when you are still in shock and still learning and at your most vulnerable that 'a lot of people choose to terminate in your situation' can wear you down.
I think the best thing you can do for someone who has a TTTS diagnosis or who knows someone is to give them the TTTS foundation's phone number or direct them to the website. Many doctors are still in the dark ages about treatment/outcomes. Which is somewhat understandable because it IS rare. Like any other rare medical problem, it's going to require a higher level of self-advocacy and education. I was very lucky to have a primary OB who did some of her residency work with Dr. DeLia (one of the world experts) and had a peri office where one of the doctors was also very knowledgable about it (and was putting together a TTTS center right at that time, it wasn't ready during my pregnancy, but it was being arranged!).
So I don't doubt that the old practices/opinions are still in play. And a lot of babies still do die from TTTS complications, particularly those that can't afford a plane ticket to a surgery center (if they qualify in severity, and they're not near one of the 4 places it's offered) or be able to pony up the cost for a surgery that some insurance plans still qualify as 'experimental'. A lot of babies do just fine and aren't discovered to have TTTS until after they're born and and the vein/artery connections are found in the placenta.
So I guess to answer your question, no...I think LESS pregnancies are terminated due to TTTS now, on the whole...but not in areas or amongst folks who don't have all the information. However, after having endured what I and my family endured, I cannot and will not judge anyone who decides to terminate a pregnancy, because I know all too well what it is like to have that kind of pressure when you are so vulnerable, and it was just happenstance that I had strong outside advocates who could counterbalance it.