Agreed. Without retcons, the entire Thrawn Trilogy, which so many fans consider sacred next to the films themselves, would basically have to be thrown out. Dark Empire as well, plus the stories in Tales from the Mos Eisley Cantina and Tales from Jabba's Palace. The Marvel Comics stories collected in "Classic Star Wars," as well. And yes, the Death Star stuff for sure... Jedi Academy Trilogy and Dark Saber. Even Shadows of the Empire takes a hit due to the Special Editions and ROTS. Stories portraying events immediately after the destruction of the Death Star II (Truce at Bakura IIRC, and probably many others) will be contradicted by the Special Editions.
Most of the stories have to contain some retcons because they build on and refer to prior EU stories. Of course that hasn't always been true. In the early days of the post-ROTJ EU a lot of the stories flat out contradicted each other, until most of the authors got together and agreed to honor each other's stories (examples: Leia and Han have one kid, but in another story they have twins... the retcon is that they had three kids; Leia in some early stories is already a very powerful Jedi second only to Luke, while in other stories she barely has any force ability at all, because she "doesn't have time for it" or some other BS; in some stories Han Solo is a major hero, while in others he's a bumbling idiot who has to be shown how to put on his own boots; in some stories Luke Skywalker is a mediocre Jedi, while half-trained lunatics and upstarts can kick his butt easily, while in others he's a demi-god who can practically rule the galaxy and defeat small armies single handed). The minimalism of the EU is also rather problematic, in that a handful of Star Destroyers or one crazed Admiral or "Dark Jedi" can threaten the "entire galaxy." Battles that decide the fate of the galaxy typically include less than a hundred ships. One could say that they are just trying to copy what was shown in the movies, but let's face it, budget constraints stopped Lucas from making a GALAXY WIDE CIVILIZATION look as big, grand and majestic as he wanted to in the classic trilogy. You can explain it by saying we're just seeing some small rebel faction that got lucky, and the gigantic battles of the clone wars are only hinted at. But the same minimalism takes over when you have EU authors insisting that the entire "Grand Army of the Republic" consisted of a few million clones (vs., amazingly, "quadrillions of droids" and yet miraculously, the clones are winning!). Some of this can be laid at Lucas' own feet of course (he has characters say 1.5 million "units" are being produced in Kamino's clone labs for the sale to the Republic and this is widely interpreted in the official literature as 1 unit = 1 soldier).
The retcons needed in one source may not be "massive" but over the entire EU yes, they really pile up. Without retcons, dozens of characters cease to exist (these lost Jedi and Sith are dead, and they can't come back in the Force, so they're gone, these ex-stormtroopers would be clones so their characters disappear, these Jedi council members we never saw or heard mentioned disappear, these clones produced by methods never shown or mentioned disappear, and thus the plots that surround these characters begin to fall apart).
That's why I say instead of trying to just keep putting band-aids all over the EU, just say it's all a bunch of legends and stories told around the camp fires by crusty old spacers and stuff after a few pints of lager, and restart it. Keep selling the old stuff as long as you want to, but restart the continuity fresh, with only the movies assumed as "true" as a foundation to build on.
Of course you have other problems, if Lucas is going to consider this TV series to be anything canon (it'll probably just be C-level, but I know some folks are hoping it'll be G-level just because Lucas is rumored to have a hand in the early episodes through writing credit or something), it'll probably introduce some contradictions of its own on the EU. Likewise with the CGI version of the Clone Wars series, if it's not exactly the same as the previously released animated series, it'll be one big contradiction. So look for more retcons!