Some of the Criterion LDs have stuff on them, not on their DVD releases. Special Features, commentaries. Some LDs have a DTS track, whereas a DVD may lack it. etc. However, the internet is killing a lot of this, as people put together fan edits, or right out rip the LDs for viewing.
Also, sometimes, LD, even with recent DVD releases, still has the best for some movies. Still, a LaserDisc release of, "One Shoe Makes it Murder", a TV Movie starring Robert Mitchum, is the best version available, though a DVD was released 2-3 years ago. Issue with the new DVD? It's cropped. TV movies, in the 80's were.... 1:33! TVs nowadays... Widescreen. So, instead of releasing it proper onto DVD, they chopped off the bottom and top of frames. Same shit people complained about, during 1:33 TV days, pan and scan, losing sides of images. But, it just goes to show, most people care not much about the image quality, or are clueless. They just want it to fill the screen.
Search around online, there are other examples out there. But, at $1-$2 a LD, take some chances, that's cheaper than some DVDs!