> But will that still be the case in 5 years time?

By 2020 I don't expect any new platform to arise that both lacks a standards-compliant web browser and manages to enforce the lack of such a web browser. I also don't expect any existing platform's browsers to regress from the degree of standards compliance that they have at this moment. There do exist several scenarios whereby web standards could stagnate over this time period:

Scenario 1: A major platform allows only a single browser, that browser being produced by the platform's parent company, and drags its feet in order to impede the standards process and promote native app development over web app development. The obvious potential candidate here is iOS, with Safari being the last major browser that has yet to commit to an "evergreen" model whereby features are quickly and regularly released. However, if ARC were to ever pose a threat to Apple's app model such that they could not somehow counter it with crippling technical constraints, it would be in their best interest to rapidly advance Safari to feature parity with other browsers. In other words, if Apple were ever faced with the decision of empowering the web vs. tacitly empowering a platform backed solely by Google, they're always going to choose the web.

Scenario 2: Chrome becomes dominant to the same degree that IE6 was once dominant. At this point anything that Google decides to implement (or to not implement) would de facto determine web standards, and just like Microsoft of old they could choose to leverage this power in order to advance a proprietary platform under their exclusive control. This is largely kept in check by Chrome's inability to exist on iOS as anything other than a thin wrapper over Safari, a situation that is unlikely to ever change (at least, I don't see any business motive to Apple making such a thing possible).

Scenario 3: Mozilla somehow loses its seat at the standards table. In the short term it may seem like Firefox can be ignored to a degree, but in the long term Mozilla is the Bismarck that keeps web standards moving forward in ways that are seen as beneficial to a majority of the vendors at the table. As long as there exist platforms with sizable userbases on which Firefox can be installed, it is in Mozilla's interest to advance the web as quickly as possible while convincing two of the big three to play along in order to undermine the remaining mutual competitor (and hence indirectly gaining an influence over that competitor's closed platform, using the browser as an attack vector). Mozilla's recent contract with Yahoo will sustain their efforts at their current levels for at least another five years, but its fate beyond that time will depend on how well FirefoxOS does at keeping Firefox from being locked out of the increasingly closed platforms of the future.

Given all of the above, I think it's safe to say that the web will continue to evolve rapidly for at least another five years, and the inexorable advance of mobile hardware will continue to close the gap between native performance and web performance (with projects like Mozilla's Servo designed to accelerate the closing of this gap). In the meantime, the biggest hurdles are the process of web app development (sorely lacking compared to native development, though there appear to be tentative steps in the right direction) and the unanswered question of how to make payment on the web as frictionless as it is on mobile (seriously, someone start working on this).