well, usually web pages are designed to be viewed using a desktop monitor and they (those monitors) are in general a lot bigger then mobile device displays; so using apps usually leads to better usability, accessibility and so on: they “translate” a standard format to a mobile format (well, more or less …I think). For example nowdays online newspapers have a classic version for ordinary devices and a mobile version for phones or whatever; actually this forum has only the classic one so it’s not so confortable to browse it with a mobile device.