People should not be laughed at for their dialects., speaking with your dialect is better than including foreigner words that kill the original language by time :)

I guess by "pure Mongolian" you mean the dialect that majority of people in Mongolia speaks, khalkh dialect, in other words. But you know, people in western part (torguud, bayad, durvud, uryanhai, hoton, zakhchin) have their own dialects, also some parts of eastern Mongolia have dialects too. So many get laughed at when they come to Ulaanbaatar. So no need to worry :) But have to say that thanks to media, dialects are disappearing. Ignorant people who doesn't understand the importance and beauty of dialects are also have to be blamed.

差别不大。主要是有腔调上的不同。还有一些新名词的翻译也是不同的。

内蒙古的蒙语和外蒙古的差别不大，基本一致，主要是说话时的腔调有不同，还有一些新词汇翻译得不一样。