Thanks to seibertron.com member JelZe GoldRabbit we have a nice comparison between the US and European packaging of the Transformers Prime line. The difference is a slightly different design and well, the size of the card:
This might be part of Hasbro's new attempt at being more environmentally friendly or it might be another cost saving method, which the European packaging always was. Furthermore Transformers Prime marks the first time that Russian is put on the packaging bringing the language count to a whooping 13 languages!