Urdu and Persian

I posed these questions in another forum. Hope to get a wider response here.

The Persian influence has been so profound over Urdu that even Arabic, when it reached Urdu, got "filtered" through the sieve of Persian phonetics. Standard spoken Urdu of the learned, like standard spoken Persian of the learned, does not differentiate between 'z' (Ò) and the different 'dh' sounds of Arabic (Ö ,Ð ,Ù). Similarly no difference in the two spoken languages between the two t's (Ê ,Ø). Also, all the three different Arabic s's (Ó, Ë ,Õ) are pronounced alike as 's'in Urdu and Persian.

However, in spite of the profound influence of Persian, Urdu somehow tries to maintain, in learned speech, the difference between 'q' and 'gh' while learned spoken Persian does not -- in Persian both become 'gh'. Similarly, while 'u' has become 'o' in spoken Persian, spoken Urdu retains 'u' as 'u' -- Persian 'khoda' is still 'khuda' in Urdu. Why is this so? Did learned Persian speech try to differentiate 'q' and 'gh' in the early (formative) days of Urdu but later gave up the effort and relented to pronouncing both as 'gh'? Also, is the change of 'u' to 'o' a relatively modern phenomenon in Persian, i.e., well after the formative days of Urdu?

Thanks and regards,
Radhakrishna Warrier