It is definitely ubiquitous. When it really comes down to it, what the arduino does is take input from its pins, reads them, then does a bit of logic based on them, and puts some output on another pin (or maybe not, if its just reading stuff from a sensor, or directing some component to behave in a certain way).

The pins themselves are the same on all boards, therefore everything is compatible. The programming interfaces can be a bit difference, but the basic logic is the same, its just figuring out what the specific call you need to make to input/output. The circuit part is exactly the same. Tutorials for the tessel are great- it actually runs something called node.js natively on the chip- its essentially javascript, but makes interacting with the web SUPER easy- I was playing with it when I first got it and had it output my apartments temperature to twitter after reading a few tutorials.

The term test component is a bit inaccurate- these are the same components that hobbyists have been using (and have been in many products you own) for years. All it really means is that the component can be driven off a 3.3 or 5v signal- which is what the arduino outputs. Saying something is arduino compatible is just marketing to make beginners feel more at ease.

However, on a slightly different topic- so a wifi chip came out called the esp8266 which you can get on ebay for about $5 which you can connect to arduino. This may be a game changer as the biggest weakness of arduinos is that it is difficult to get data into and out of them- you essentially have to use extra hardware to get data into or out of them. This could change all of that. For instance, lets say I wanted to adjust the moisture level where my solenoid turns on/off. Right now I have to reprogram the arduino. But with wifi I could potentially just send it a signal from my phone or computer. Similarly you could be tracking your moisture/temp/light levels from a webpage or have them emailed or whatever.

Anyway, I went off on a huge tangent, but the answer is yes, there are good tutorials and components for the other boards. You can take a look at tessel's docs here: http://start.tessel.io/start

Be warned though that the original tessel has very flakey wifi- to the point where you can't really use it for anything important. They are fixing that w/ the Tessel 2 which is now available for preorder (and about 1/3 the price of the original tessel).