I suspect that english has been made easier for non-native speakers by a rich recent history of english being spoken by non-native speakers (particularly in America). This may have broken down expectations about the language that native english speakers have.
For example, a native english speaker will not have much difficulty at all when they encounter an Russian who speaks english as a second language and frequently miss or misuse articles. Although the native Russian speaker is technically using the english language incorrectly, native english speakers have adapted to expect and tolerate a very high rate of errors. This lowers the level of language perfection that is necessary to effectively communicate in english.
Speakers of languages without this sort of recent tradition of non-native speakers may find grammatical errors more jarring, because they have been exposed to them less often.
For example, a native english speaker will not have much difficulty at all when they encounter an Russian who speaks english as a second language and frequently miss or misuse articles. Although the native Russian speaker is technically using the english language incorrectly, native english speakers have adapted to expect and tolerate a very high rate of errors. This lowers the level of language perfection that is necessary to effectively communicate in english.
Speakers of languages without this sort of recent tradition of non-native speakers may find grammatical errors more jarring, because they have been exposed to them less often.