I think the key word is "temporarily" until some percentage of those working poor get laid off and then inflationary pressures make $10/hour the new $5.  Or maybe it's just a sneaky backhanded way to increase payroll taxes? 

My first thought was that yes this would increase payroll taxes.

But it also would mean fewer government subsidies to people earning poverty wages because fewer people would be earning poverty wages.

Walmart alone is costing $900k to $1.8mm per year PER STORE:

http://pandawhale.com/post/20792/a-new-report-claims-that-wal-marts-wages-could-be-costing-taxpayers-900000-to-175-million-per-year-per-store

Cost isn't quite the right word.  Walmart alone is saving people tens of millions of dollars per store which is money that goes straight back into people's pockets, including the working poor, for things they really need and at the time they need them.  

But so is Amazon, and they manage to pay their fulfillment center workers a decent wage, right?

Yes but there are many fewer of them than Walmart workers.

Imagine replacing 100,000 store workers with 10,000 fulfillment center workers.

The 10,000 make more but 90,000 are unemployed.

Walmart has the potential to have both in-store workers and fulfillment center workers:

http://pandawhale.com/post/22509/walmart-vs-amazon-its-about-to-get-interesting-forbes

The more fulfillment center workers they have, the fewer in-store workers they need.