Of course, other classes bring some similar abilities to raid as well. Druids and death knights can resurrect other players in battle, and buffs can be gotten from nearly every other class, particularly various hunter pets. Priests do have the ability to place a Lightwell, which has a similar thrust behind it as Healthstones, but let's face it: a Healthstone is superior in terms of immediate useability and convenience. As for portals and the summoning ... there aren't any real other equivalents to either of those. Summoning has been a defining trait of the warlock class for a very long time now, since way back in WoW's original incarnation.
Our own Matticus told us about how his guild used to have a warlock deployed at each of the world dragon spawn points, for (relatively) quick raid assemblage if needed. Curses used to be arranged differently, too. For example, Curse of Tongues was removed and its function rolled into into Curse of Enfeeblement, instead. Once upon a time Mortal Coil was called Death Coil, and added a self-heal as well. And Healthstones! Healthstones used to be a multi-point talent, and would heal for different amounts depending on the number of points put into the talent, for up to three different Healthstone sizes. It wasn't uncommon for three warlocks in a guild to each talent differently, so every raid member could have a Healthstone of each size. Nowadays you get one Healthstone with three charges, of course.
I can see what Ghostcrawler means by saying that warlocks may bring too much utility to raids, but, at the same time, I like all the stuff they bring and really wouldn't want to give up Healthstones, or Soulstones, or portals or anything like that. What about you? Do you (as I do) love your raid warlock and want only the best for them? Or would you like to see some more warlock utility go by the wayside so you can play a different toon, or bring a different toon to your raid? Do you not care about them in PvE but just hate their guts in PvP? Tell us all about it!