Half of their take in the first session was from that one book. If I remember correctly, comics/comic art comprise about 4% of their yearly sales. I'm sure Heritage wants to be players in as many collectible/antique markets as they can, including movie paper.
One thing to consider about slabbing books like the Tec 27 is that the stories inside have been reprinted dozens of times. Granted, there's nothing like opening and paging through a vintage book, but if you had a poster worth 1M would you have it archivally framed or would unroll & roll it every time you wanted to show it off? When you get into six-figure and up territory, you have to think about preservation. If you should have a mishap that results in damage, it doesn't affect the poster as restoration isn't frowned upon as much as in comics. If this comic was raw (unslabbed) and suffered damage, the grade - consequently the price - would go down. And if the owner opted to get the damage addressed by a restorer, the book would be worth 1/2 to 1/4 what it is now. Also, CGC has given people the confidence that the book doesn't have any hidden restoration (remember what I just said about the value of restored books). There are enough stories about unscrupulous people selling high value comics, with undisclosed resto, as unrestored. Unfortunately, quite a few people only found out about the resto after they sent their books to CGC, like the owner of
this book. I know of quite a few collectors that buy slabbed books, crack them out and read them. Hell, I paged through a friend's copy of Action 1 (yes, it's an authentic copy of the book) and it was an amazing experience as I hadn't held a real one before. I was scared to death as I knew it was worth a bundle, but my friend was like "Don't worry about it. The book is extensively restored. You can't do anything to it that can't be fixed." Aside from the Superman story, most of the other stories are in b&w (monochrome, for our UK friends). I never knew that as those stories are never included in reprints, so I have an appreciation for raw books. But I also understand that once you get into that rarified air, collectibles sometimes become commodities. As such, preservation takes priority above all else.