The "surprise," if there is one, is that exposed water ice at Mars' south pole eluded direct detection for so long. One might note that water ice was directly remotely sensed over the northern polar cap as far back as Viking.
That said, many scientists suspected that water ice was a consituent of the martian south polar cap for a variety of reasons (e.g., morphology of erosional forms, i.e., "Swiss cheese pits," support a two layer model, as do strength and deformation arguments of a polar cap composed entirely of frozen CO2). However, to date there was no direct evidence until the the GRS suite aboard 2001 Mars Odyssey began returning data indicating much more hydrogen deposits than expected based on previous data, though water ice in this instance was only inferred. The work of Titus et al. is, in a sense, confirmatory.

Alex R. Blackwell
University of Hawaii