Hi Ledu,
thanks for this interesting observation. Dialogues without question marks may indeed be more common in Chinese, perhaps also because you can make mild suggestions using particles like 吧 at the end of a sentence, which implicitly ask for a reply but don't require a question mark. Or there's the 啊 particle which also often asks for an answer/confirmation without a question mark.
This difference might also be due to the fact that Chinese needs to be less grammar-focused than most Western languages. Western languages in my feeling tend to construct their meanings more through sentence-building, whereas Chinese can rely on the expressive power of each Chinese character, each word can stand by itself more, and it ideally has shorter sentences (or shorter clauses). Western languages with their many word inflections (such as in Spanish or Italian) and cases thus need to be a lot more rigid grammatically to prevent sentences from falling apart, which includes rules about adding commas (German is probably the leader here.) and a requirement for question marks when questions are asked.
The above is based on my own experience and some bits of information I've picked up. It would be interesting to read more about these differences in constructing meaning, though it would have to be a highly subjective treatise, as these observations are pretty difficult to back up by objective scientific consensus.
Keep your impressions coming! I wonder if others could add to this.
Cheers,
Shun