You will need to show specific examples as the microsoft home page is fully responsive.
The yahoo page is fully mobile when accessed via mobile.
Craigs list also shows differently on mobile.
The last two are not responsive on desktop but are fully optimised when accessed by mobile. Large companies have the facilities to maintain two separate sites one for desktop and one for mobile but many others will create responsive sites (like the microsoft page). There are always exceptions of course.
Indeed I would go as far to say that most large companies worth their salt have optimised for mobile although some will be better than others.
The stats show that you should ignore mobile at your peril just as high street stores that have not embraced internet shopping are all failing.
The fact is that mobile usage on the internet surpassed desktop usage some time ago and most internet visits these days are via a mobile device or tablet.