Confused ji,
I am not sure where they are getting that from. You'll notice it's only householder Sikhs saying that. This is the "householder bias" on the internet. You don't hear from Nihangs or Udasis as they are monks and ascetics, they live such a lifestyle where they don't have computers...
Gursikhs possess the qualities of both a householder and renunciate. - 131
One who knows God is approved whether he is a householder or a renunciate. - 385, 1329
A true householder, a true renunciate is one who recognizes his own Self. - 1332
Nope no marked difference in Sikh teachings. The teachings for them and lay persons are the same as laid out in Sri Guru Granth Sahib Ji and Dasam Granth. Although, sometimes Gurus do speak to renunciates and householders separately.
There is an additional strict code of conduct for Khalsa and Nihangs and that is the rehitnama. Nihangs also have another text that they venerate, namely Sarbloh Granth. I don't know much about this text.
Don't know of any such codes for Udasis. They probably do have their own code.
Yes the idea of simplicity is very well related to the idea of renunciation. This is the real reason for not cutting hair. Apparently, the exact same reason is also the reason for cutting hair. The world is an odd place indeed.
Sikhs did not always wear turbans, they simply covered their hair with caps (seli topi). This tradition was started by the sixth Guru, who on his ceremony of receiving Guruship asked Baba Buddha ji to place a turban and plume on his head rather than a cap. The sixth Guru and tenth Guru saw these caps as the symbol of pacifism and slavery and urged all warriors to wear turbans. They themselves wore turbans.
Udasis who existed prior to the guruship of the sixth Guru did/do not wear turbans but Nihangs, on the other hand, come from the time of the sixth Guru and so they wear turbans. Now during the rule of the tenth Guru, we an increasing number of Shaivite recruits in the army. This lead to a distinct Nihang turban style and symbolism.
Easier is not an issue for monks. Monks aren't necessarily looking for easy things. Both are quite practical. Hence why we see both.
Well mark of monkhood is one practical purpose. Another is simplicity. Another is a mark of renunciation and detachment.
These are all practical purposes.
The reasons for keeping of hair are the same reason why renunciates/ascetics keep hair - simplicity and detachment from the world.
