Traditionally European TV sets have been more forgiving than their US counterparts, accepting NTSC "nudged" into PAL-60 or NTSC 4.43 in the analog realm.
While the transition to HD did unify the display resolutions and pixel aspect ratios (everything's square, yay!), the differences in refresh/sampling rates remained.
One day my friend, one day... everything will be 600 Hz or better so 24, 25, 30, 50 and 60 fps content will all be supported and play without judder or needing interpolation.
So back to the topic at hand, it's possible the OP's TV doesn't know what to do with a 30/60 Hz input from Chromecast, though that would be quite silly of LG to impose such a restriction. Still, silly happens more often than you think for all kinds of reasons (gray market sales due to varying exchange rates and import/export laws often is a concern, as we burden on regional support that got no revenue from the foreign sale).
TBH, I don't know for certain whether Chromecast is capable of 25/50 Hz output, it might be. But being that Google isn't selling it outside of US/Canada yet, I doubt they've tested it.
>> Anybody in Europe, can you confirm me whether Chromecast outputs 720/50p, 1080/50i or 1080/50p to your TV? <<