Same Result For Various Devices
Website is not some abstract and incorporeal substance, but exactly material entity!
As for seeming intangibility of the website or software in general, it is possible to draw logical parallels. We all know such a thing as money! What is $100? Is it banknote of hundred dollars worth or a hundred of one dollar coins, or just a check, or even digits on the screen when we use our client-bank application? It is not hard to quess, money also not directly tangible but only by means of its projection to the phisical world (banknotes, coins, checks etc.) Web-projects is similar to money in this aspect, becase they made from more subtle matter compare to wood or steel. But we can see and feel it on the screens of various gadgets, paper copies, listen its audio version (for example, by means of software for blind people).
In view of the above, modern website design approach completely different from poly graphic design and closer to engineering design of physical devices with drawings and blueprints.
Modern website design must be responsive and work correctly not depending on device we use for viewing it