No its not, but most of them dont have fast enough download speeds or monthly data limits to allow purchasing on Steam and downloading every game purchased to be possible.
In the Uk for example, you can get what is advertised as a 20 Mbps Unlimited broadband for £.7.50 pm.
However, in the fine print, they apply a fair use policy and cap your data usage to just 40 Gb per month. They are still allowed to advertise this as unlimited because they dont charge you any extra for going over it, but if you exceed that limit for too many months, they can cripple your maximum speed to 64 kbps.
Also, while it is advertised as 20 Mbps, most people who dont live near to the ISP will still only get around 1-4 Mbps speed as I do, with download sppeds fluctuating from 300-600 Kbps, and hardly ever anymore. It is still a lot more convenient, and faster to buy and install games from CD / DVD than it is to digitally download them for most people.
Even in this day and age, 'reliable internet' depends entirely on where you live. Sure america has it, but dont assume that the rest of the world also does. Broadband services in the UK are far from reliable and very very slow compared to what you should be getting as advertised on your broadband deal.