Hey ArenaNet, I heard you like money. Every company likes money.
So why not implementing a web frontend for the good ol' Gem Store? I'm quite sure that your revenue will skyrocket, if you offer a service like this. And here's the reason:
There are two ways to play Guild Wars 2:
1.) Playing the actual game
Sure, if you're playing the game, you're playing the game. Running around, killing stuff, checking ah, doing fractals, etc, etc, you know the stories.
2.) Playing the "meta game"
Everybody will agree, that there is a whole "meta game" around Guild Wars 2, where people are doing things like
I'm quite sure that this "meta game" is played by a big bunch of players all day long and on all devices they own. At work, at school, in bed, heck even on the toilet! I even dare to maintain, that a big fraction of the player base spend more time on the "meta game" than actually ingame.
To flesh out this example:
Imagine a dad who works at the office. His time to play the actual game is really limited to the evening hours, when the kids are in bed and his wife is doing whatever she likes. But.... he's got little preserved time slots during the whole day, where he plays the "meta game". Checks a new build in the lunch break. Tries to find the next cool pistol-skin on the bus. You get the picture. So, he's actuallay preparing himself over the whole day, to get the best out the 1-2 hours in the evening playing the game. I think, this scenario is quite common among a big part of the player base.
Now, where's the connection to a Web Gem Store? I think people are propably (even more!) willing to spend money on the game during the "meta game"! Why? Because it's their only way to interact with the game while not being ingame. They already spent hours after hours (cumulated!) researching a new cool raptor skin. Or laying out a plan to craft a legendary weapon, but inventory space is too limited. Following the AIDA-Principle of marketing, you've already got their ATTENTION, INTEREST and DESIRE. All that's left is enabling the ACTION. And this is where a Web Gem Store will shine: by using the Web Gem Store, people are able to satisfy their urge to "do something" for their character. And you, ArenaNet, are making money.
Living in an age of multichannel & omnichannel e-commerce, people are naturally expecting, that they are able to buy wares on all channels and devices. Not being able to do so, will limit your ways to generate revenue and leaves the customer unsatisfied.
So! Looking forward buying my stuff on my mobile!
[On a side note: I wouldn't mind being able to do ALL stuff, that's NOT actually killing things, on my mobile, like: using the AH, gearing my toon, speccing my build, managing my bank and my inventory, etc. - all this stuff leaves me engaged with the game. And this is the first step towards a transaction.]