The statements of Nicola von Hammerstein of the Max Planck Society (MPG) in
In fact, however, the MPG's Rudiger Willems admitted in a letter to the editor of
The European Commission has already stated that: "EU nationals have the right to work in other Member States (Article 39 of the EC Treaty). This right to free movement of workers includes the right to have equal access to jobs and equal treatment in relation to working conditions as compared to the nationals of the host Member State. On the basis of Article 39 nationals of other Member States must, therefore, be allowed to apply for research positions for which an employment contract is offered (like the positions under BAT IIa/2 as concerned in the written question) at the German Max Planck Society in the same way as German nationals."3
Had the MPG policy not been discriminatory, as Von Hammerstein claimed, then there would have been no need to for the MPG to replace their old rules4 with those mentioned in your article. Whether things will change in practice remains to be seen.
Among other things, a contract provides higher net wages, health insurance, unemployment benefits, and a retirement plan contribution. Only the last item needs to be transferred if one leaves Germany, and this transfer is possible to any EU country and to the many countries that have a joint social security agreement with Germany.
I know of no case in which a fully informed student was offered a contract but declined, preferring the poorer conditions of a stipend. Von Hammerstein should provide evidence to support her extraordinary claim that "many students do not want to pay into the German pension and unemployment insurance system if they are in Germany for only a relatively short time."