Just my 2cents. I don't trust Ikea tables at all. Most of their stuff is made of particle board with a layer of laminate on top. Initially i was going to use an Ikea table for my 30 gallon. But after reading the specs on all their tables It was too risky for my liking.
If you go to the store and look at their product tags or go on-line and read the product Specs you will quickly see that they are not made for anything heavy. I would rather be safe then have a 20 gallon tank break on the floor.
With the specific table you linked I would highly suggest not to use it for a 20 gallon long. Firstly, by the looks of it there are no support beams in the centre. Meaning that it's only held up by the sides. and Secondly, if that table is made from particle board the small legs might cause issue at the bottom.
For example (in the link below) something like this looks really study. But once again it's made of particle board. The product specs it's rated only a max weight of 15kg or 33lbs. And trust me your 20 gallon is will be 150lbs +
http://www.ikea.com/ca/en/catalog/products/40207169/