[Lord of Nukes]

Yes their extra armor in Brood War is a great asset. If your opponent is going with mostly ground which happens more often than not versus Zerg due to Scourge, Devourers, and Plague, the Ultralisk surviving from a lot of damage is incredibly useful. A large squad of Marines with Stim Pack and Medics that would decimate a swarm of Zerglings can go down quite easily to a pack of Ultralisk with Zerglings; or as ArtOfProtoss said, against Dragoons. Maelstrom and Psionic Storm can be very painful to both your Ultralisks and your Zerglings, so you may want to bring Queens with you if you can afford them and their respective technologies.