By the same argument, customers are paying the costs for Best Buy's internal logistics and retail floor operations to enable “free browse and instant pickup”. If those costs are higher than Amazon/NewEgg's costs for "free shipping", I'd expect to see exactly the relative prices that you're seeing.
I'll reiterate my point that shipping is a cost that has to be paid, but who bears that cost is not necessarily the customer. If it was the case that the customer was the one bearing that cost, there would be a difference in the price you pay for goods at a physical store vs. goods shipped to your home, implicitly or explicitly. There is generally no difference, and in many cases, ship to home is cheaper because you can select from more retailers.
In the larger discussion of payroll taxes, to disprove that workers bear the entire burden of payroll taxes, just go through the thought experiment where we eliminate the employer side of the SS tax and whether wages would rise 6.2%. They wouldn't. Workers were willing to work for $N previously, there is no reason that they would stop working/change jobs unless they were paid $N + 6.2%.
But now do the thought experiment where the employee must explicitly pay the extra 6.2%. Now of course you have to give them a 6.2% raise, because they would demand it to cover their increased costs.
Numbers: I pay the worker $10000 a month. Let's say my tax cost is $500 a month, and their tax cost is $500/mo. So they get a check for $9500, they see a $500 tax deduction, and they net $9000.
My all in cost is $10000.
Now the city says "you don't have to pay your part of the tax anymore, the worker does!"
So now I pay them $10000, they see a deduction of $1000 on their paycheck, and net $9000. My all in cost is still $10000, their net is still $9000. Nothing has changed.
I'm still paying $10000 to have that worker. And if my budget is 100000, I can still only afford 10 workers.
That's how every business works. All per employee costs are borne by the employee one way or another.