I'm with Locutus, I like the mIRC default colours and layout, they suit me fine, and I'm sure many others too. I would never consider using a skin - except if he did in fact change the layout.
The looks of buttons and/or windows looks different depending on what OS you have - mIRC on Win XP looks so much better than mIRC on Win 98 (in my opinion anyway, seeing as I used to have '98).
And anyway, I don't use mIRC because it's popular...I use it because I like it more than other clients. This is not to say other clients are not good, I think Klient is very good and the author is very nice etc etc, but it's not for me. Sure, when I first downloaded mIRC it was because it was the only IRC client I had even heard of..but now, thing's have changed.
I'm confident mIRC has more than 5 years left in it, however, I'm sure Khaled is aware that not everything lasts forever.