Speaking as a US civilian who was an adult at the time of Desert Storm: we were certainly led to the expectation that there would be heavy casualties in breaching the "Saddam Line". We were told that the Iraqi army was well trained and battle hardened due to their long war with Iran, and were unlikely to surrender and it was likely to be a slugfest. All of this turned out not to be true, but it's unclear what was in the mind of the Allied commanders.

Note, as civilians we knew of the long allied bombardment of Iraqi positions, but also, at least those of us who had read about air power, were unsure of its effect on deeply entrenched troops. We also did not know about the "Left Hook" operation where US VII Corps and UK 1st Armoured Division as well as Airborne and French units went around most Iraqi positions to the west, bypassing the heaviest defenses. However, 1st Marine Division did attack straight into Kuwait, and overwhelmed Iraqi defenses in short order, taking low casualties.

In sum, for us observing from home, it was a blessed surprise that casualties were so low. "Jarhead" did not make that up out of whole cloth. What the Allied command thought they would be is unknown to me, but if I were them, I would have prepared people for the heavy casualty, worst-case scenario.

Edit: a word.