Now this is all true - to an extent. And it is probably indeed all you need to know if you're planning a one-time short trip to Japan. But if you're staying any longer, or even planning to return on any kind of regular basis, it pays to know that there is another, less conspicuous currency running underneath all this - points.
Of course, loyalty cards, air miles, rewards points etc. are a global phenomenon, and many merchants all over the world offer some form of a return for their regular customers. The Japanese have just elevated this to a whole new level.
Every supermarket, every drug store, every clothing store, every convenience store - you name it, they have a points system. Amazon Japan, unlike its global counterparts, has also jumped on the bandwagon to offer points with purchases. So far, not so unusual, you say. Okay - some banks have point systems and will pay you to use their ATMs, or just to sign in to their online banking interface. Good? It gets better. Utilities companies - that's right, your gas, water, electricity bills - will earn you points, either directly from the companies for the money you pay to them, or again from your bank for setting up a monthly direct debit. Even some delivery services - for instance, that courier company Yamato with the cute black cat logo will actually give you a choice of 3 different points systems on which you can get your rewards for sending or receiving stuff with them.
And if you *really* want to get weird about it, how about meta-points - websites that seem to give you bonus points just for clicking through to online shopping sites through their interface, where you then collect points for your shopping as usual. That's some aggressive advertising if you ask me!
If all of this sounds too confusing, or just too much trouble to bother with, I'll run you through an example system that I have at the moment. Of all the different points systems that I've encountered, by far the most lucrative is Rakuten, which I've written about before. I'm subscribed to their mobile service (points for paying my bill), and have their credit card (points for buying anything with it). Where it gets pretty awesome is if I buy anything from the Rakuten Marketplace - an eBay-equivalent selling everything under the sun - I then get extra points, on top of what I'm actually spending, simply because I'm paying with their credit card and subscribing to their mobile service. Depending on how much time you're willing to sink into this, Rakuten also runs countless promotional campaigns, which will net you point for answering questionaires, checking out partner websites, playing games... In a word, it's addictive - and well-paying - in just one month I've amassed over 9000 points - that's nearly $90 worth of free stuff!
My second most active points account is Waon, the points system run by the department store giant Aeon. I feed myself and furnish my flat out of Aeon, so it makes perfect sense for me to carry their bit of plastic around. Unlike many other systems, however, Aeon only gives you 1 point per 200 yen spent (the common rate is 1 point:100 yen) unless you use their credit card, so unless you buy into that (or, in my case, don't get your application rejected) it will be a bit slower to grow; on the plus side, many merchants attached to an Aeon complex, e.g. Daiso, or Sports Authority, will also offer Waon points. Fingers crossed, it won't take much longer for me to get a week's worth of groceries for free!
Then there is the T card, which is arguably one of the most widely used, and hence most versatile, point systems. The originating merchant for the T card is Tsutaya, a bookstore, but I got mine from a Family Mart convenience store instead. You can spend and collect T points at any of a long list of partner companies - even some stores that have their own points system will issue T points instead on your request (though at a lower rate), and I've see the ubiquitous T logo hanging in taxi windows. Personally, though, my T points have mostly come through my bank - Shinsei allows you to collect a small monthly quota of points for doing all those little bank things that you would do anyway, as mentioned above. Literally without any expenditure on my part, I can get myself a little treat every few months just for banking smartly.
I'll admit there are cons to these systems - most of them are fairly dependent on long-term use, such as credit cards or subscriptions, to be fully effective. The sheer number of different systems also has a tendency to lock you into spending with a dozen different merchants just to try and get something out of the points. But if you do find yourself shopping regularly in Japan, I would argue that it would be silly to ignore these for any significant amount of time - just being aware of what's available, and then picking the ones that work best for you, can give you a pleasant surprise in an unexpectedly short period of time.