First of all, I have very little religious knowledge, so this is mostly my impression.
In Muslim cultures, there are two aspects: what is required (farz) and what is recommended/suggested/expected (sunnah).
The first part (required) comes from what is explicitly written in the Quran because the Quran is considered the word of God. The second part (recommended) usually involves emulating the customs and rituals of Prophet Muhammad (PBUH), his family and his companions. These are obviously Arabic customs and some of them even predate Islam. They were just part of contemporary Arabic culture during the Prophet's (PBUH) lifetime.
On the required part, Islam requires both men and women to dress modestly and to avoid sexualized display. I don't know if there are any specific dress codes in the Quran.
The dress codes, and the beard for men, is mostly sunnah, as far as I know. Over the years, customs have a habit of becoming an essential part of any culture. This is true around the world, not just Muslims.
Someone else can correct if I am wrong.