Let me try to explain it a little more detailed.

My main problem: "But the problem appears in Safari which
doesn't accept .gz file type extension", which means although we have enabled gziping on nginx and it's working on Chrome perfectly (we know this looking at network tab in developer tools, where we can see the size of the gzipped file one.dds that needed to be downloaded and it's around 2MB while the original one.dds filesize is around 4MB). I also checkede the header of the file, and Accept-Encoding has values GZIP, deflate, sdch.

But the same file loaded on iMac with Safari browser takes/loads 4MB, which clearly states that the Safari somehow doesn't accept or ignores files with .gz extension. I also checked file header and Accept-Encoding has: GZIP, deflate.

The same problems were already reported on some other forums, but they were able to solve the problem, because they're using Apache, which enables adding options as:
AddEncoding gzip .jsz
AddType text/javascript .jsz

I hope this links will help you understand my problem:
http://blog.bigsmoke.us/2012/01/16/safari-ignores-content-type-for-gz-suffix
http://stackoverflow.com/questions/962721/pre-compressed-gzip-break-on-chrome-why

regards,
m