[latk]

The site does explain its methodology.

By default, it shows the costs when using the cheapest post-paid plan with at least 500MB allowance for at least 30 days – cheapest in absolute terms, not per GB.

You can toggle the option to show prepaid plans with the same parameters (at least 500 MB for at least 30 days).

But since it takes data from the ITU and not from the real market, the numbers do indeed seem inflated. One of the cheapest (in absolute terms) prepaid plans for mobile internet in Germany is AldiTalk at 4€/1GB/4 weeks, so that the pageload should cost even less than 1ct (0.0056 EUR). Similarly, your Telekom plans are for 4 weeks. Maybe they've excluded these plan because it's not for at least 30 days.

[Ajedi32]

The problem with that methodology is that the cheapest plans in terms of cost/month are actually likely to be the most expensive in terms of cost/GB.

If a service provider offers a $20/month plan with 500 MB of data, their $40/month plan will almost certainly offer a lot more than 1000 MB. The cheapest plans are usually designed specifically for people who don't plan to use a significant amount of data.

[tobyjsullivan]

Alternatively you could argue that the cheapest plans are targeted at people who have the least money to spend on wireless data. It seems reasonable that these are the people who would be most sensitive to the unit cost of accessing a single website.

[ketzu]

One possible reason is that 4 weeks are 28 days, which is less than 30 days, their minimum.