Most of the more restrictive EU countries (e.g.: UK, Ireland, etc.) have barriers to getting immigration stamps, which the most oft way of immigration is through employment and the most labour available to foreigners is either tech or medicine.
For example, in Sweden, a position must be listed as a highly qualified skill, the role must be listed for 20 days (I think it is) - so that EU citizens can be afforded an opportunity before the role is given to an immigrant, and then the employment contract must be agreed upon by the labour union before it can be approved.
You're not getting an employment contract, for example, to work in Burger King in Stockholm because it wouldn't pass the labour market needs test.
So, this is presumably why the OC thinks that medicine and tech make you immigration eligible.
Worthy of note is that tech or medicine are the best ways to get the EU Blue card (the equivalent of the US Greencard); so, the assumption isn't without its merits.