The history of Mars water and why we need people on Mars...
It must take a special mentality to be a space scientist.
Regarding water on Mars: First there was no water and never was and then well, maybe there used to be some a long time ago but it was really salty and couldn't support life. ...Oh well maybe there was more water than that but it is all gone and wasn't around long enough for life to develop, etc. To make a long story short it seems like now you can't go to Mars without tripping over water. There are some that argue that even the rovers scraped the covering dirt off of some briny water (It must be briny because there can't be THAT much water, right?)
All these probes are purpose built and that purpose is based on the prevailing scientific opinion 4-10 years before launch so why would anyone build a probe that can look for life? Optimal launch windows occur approx. every 26 months but the real turnaround in scientific thinking takes around a decade as probe designs get revised which means that some time around 2020 we may have a probe that can begin to look for life signs - assuming that researchers are willing to fly in the face of conventional wisdom (there is no life on Mars after all) and invest in a risky discovery mission.
Now about that scientific mindset - Let us presume that there is a higher incidence of atheism among exobiology researchers, it is monumentally ironic that they are willing to extend research by minute incremental steps (the word 'pedestrian' hardly begins to describe this pace of research) every decade or so. Many current researchers will be Dead (capitalized to emphasize their lack of afterlife) and only remembered in dusty mission reports in a universe that, for them, ceases to exist when they die. Legacies are for people that believe in spiritual continuity yet these people labour away knowing that they will never see the real fruits of their labours.
On the other hand some astro-johny on the spot - even a square jawed military poster boy - could pick up the rock with the green scunge and comment, "Crikey, maybe we should stick this under a 'scope and 'ave a look." Then all those scientists could knock off early and rest up to really kick it at the post-Nobel party.