I was going to say the same thing. I would bet that there is a lot of jet.com tech and expertise now in Walmart.com.
Then see what WalMart's ecommerce growth was before Marc Lore
and what it is now after Marc Lore
Perhaps the single biggest factor that it is growing fast is that they got the CEO/Founder of Diapers.com and Jet.com to come help them understand ecommerce