Assuming all things being equal... The only difference I can see is server bandwidth.
The likes of Nike and other conglomerate organisations, probably have the requisite cash reserves to host their websites on server architectures you and I can only dream of.
Think of it like you ordering 1000 do-nuts. The websites hosting you and I would use consists of one guy behind the counter having to dish up 1000 do-nuts...It would take him a long time right? Now Nike/google probably have 10,000 guys behind the counter. It wouldn't take them any time at all to dish up 1000 do-nuts.
A way to achieve a similar effect would be to dramatically reduce the image quality resolution...and have a preloader which waits to load all the images before bringing up the page.