Well, both were in a way betrayed by Angel. Lindsey risked his life to help Angel's plan and then was killed by, literally, as he said, "a flunky." I mean, really, what sense did it make to kill him at that point? He could have been at least as much help in the final battle as Gunn, even unwounded, and Angel had pretty much resigned himself to nobody surviving the night alive. Another sword would've increased his fighting force by 20%, nothing to throw away lightly. If worse came to worst, Angel could have killed him himself at any time during the battle. It would have been the honorable thing to do. At least he would have allowed Lindsey to die with some sense of dignity. The way it worked out was just like Angel telling Lindsey that Lindsey was beneath him. (Does that sound familiar?)
As for Lorne, how could Angel forget that he was an EMPATH, for god's sake? Granted, he couldn't fully "read" Lindsey unless he sang, and that was hardly the time to break into song, but he must have felt SOME degree of Lindsey's pain, sense of betrayal and death. Something like that must have been truly horrible and heart breaking for both of them.
It's just yet one more example of Angel's total unconcern for the people who literally placed their lives in his hands. The assault was hastily and poorly planned (I know, both the season AND the series was ending, but some more time could have found somewhere to allow for a better strategy AND the gathering of more allies.) One wasted episode that could have been dropped in order to have more prep time was "The Girl In Question." It contributed absolutely nothing to the continuity of the series except to get Spike a new supply of leather dusters, and as we know now, it wasn't even Buffy. When Sarah said that she wouldn't be available for a guest shot on the show, the whole episode should have been scrapped in favor of allowing the writers more time to set the stage for the big finale. If they were going to use a poor substitute for Buffy anyway, they could've saved it for the end, then either shown her back at the head of a band of Slayers coming up behind Spike, Angel, and Illyria in the last scene, or on the other end of a phone call when one or both of her vampire lovers called to say what they honestly thought was goodbye.