The web platform is rapidly improving for games, on all fronts.
The HTML5 offline (appcache) spec allows you to have resources available when offline (and you don't need to write your own code to stuff things into localstorage...) Besides, localstorage is not considered, by browser hackers, to be the best idea performance-wise. They recommend IndexedDB.
Those specifics aside, my main point is to say that game makers are targeting the browser and browser vendors are very much aware of the pain points they have and are working to correct them. Browsers today evolve much faster than they did a few years ago.
The HTML5 offline (appcache) spec allows you to have resources available when offline (and you don't need to write your own code to stuff things into localstorage...) Besides, localstorage is not considered, by browser hackers, to be the best idea performance-wise. They recommend IndexedDB.
Those specifics aside, my main point is to say that game makers are targeting the browser and browser vendors are very much aware of the pain points they have and are working to correct them. Browsers today evolve much faster than they did a few years ago.
(obdisclaimer: I work for Mozilla)