The exact wording of that comment is (regarding the spherules)
"We have observed the following properties:
• Dominantly spherical or sub-spherical.
• Some are split, and can exhibit angular or irregular shapes.
• Appear loose on top of outcrop materials, plains units, and crater interiors (Figure 1).
• Appear in various stages of erosion from within outcrop materials (Figure 2).
• Cross layers within finely bedded sedimentary structures.
• Are split by fractures in surrounding host rock.
• Occur primarily as single berries, but can be connected as composite grains or strings.
• Occasional presence of latitudinal grooves either parallel or at an angle to bedding.
• Surrounding sediment is more coarsely crystalline than in the outcrops in general.
• Appear weathered and in some cases coated by brighter materials.
• Are not aggregated along bedding planes, which might be expected for lapilli or impact sphereules.
(from “BLUEBERRIES”: A SUMMARY OF THE HEMATITE CONCRETIONS FOUND AT THE OPPORTUNITY LANDING SITE. W. Calvin eta l, )
www.lpi.usra.edu/meetings/earlymars2004/pdf/8074.pdf
I also think it is a critical observation for a model that has a coating of frozen volatiles (HCl, H2SO4, etc) deposited over basaltic dust then slowly reacting. Possibly daily warming allows the reaction to progress and over time all the acid is consumed. and product water lost by sublimation or into water of crystalization. Such a slow process is not seen on earth due to over-supply of water but is possible on Mars. Such a model is in accord with formation of jarosite (see this weeks Nature) and with the lack of changes in trace element ratios between fresh and altered rocks.