I think that has a source: NTFS is hard to implement.
File Permissions are per-FS-base. You dont have to use the same permissions on all disks just because you use that on one.
While ext3 supports custom permissions too, so all this could be added
"More *NIX like: /mnt/c" - thats not more unix like. /mnt ist just one of many ideas where to mount your external mounts

if you want it *NIX like, you have to make it user-editable. thats what is all about (linux is about choices). And AFAIK UNIX in special dont use /mnt, its something linux specific, but dont nail me up on that =)
but thats going off-topic. of course I would suggest to use /mnt instead of /win in standard. but best would be to use /reactos/mnt/c. why? so u can install reactos parallel to linux. or maybe: keep it up to the user, to change that.
As I said, NTFS would be adorable, but seriously:
* nobody would use ReactOS in early stages on servers, so it is not very important to have NTFS before anything else
* the bigger part of the community will grow from the sector "between linux and windows" - people who hate to be stuck in the "superOS" but cant change to linux completely. they dont need ntfs hardly.
* ext3 is better documented. early readwrite of ext and fat and readonly for ntfs would conclude in increasing usage of this file systems. which means, users, who want to use reactos on servers, will think about using ext3 instead of ntfs. and thats a good choice, because ntfs doesnt have anything inside, ext3 cant do. and: ntfs is SLOW in comparison. ext3 is hell of a fast filesystem, while fat is still faster than ntfs.