Could you expand how Square is different market segment? I thought POS terminal was one of their primary products.

Square is for small or entry level merchants who may be in their first year and can't afford an actual production grade POS or web integration, stripe is for those who've realized they've reached that point or have encountered Square's limits, and by them moving into the entry level market by supporting this method of transacting with iDevices, I'd say square should be considering their next move.

In what way would you consider merchants to be scale-bifurcated along the card-present/e-commerce line?

At my local farmers market every vendor uses Square to accept payments, but also seems to have iPhones themselves.

With this announcement I can very much see Square being removed from the equation in this small business without fixed store front scenario.