Pakistan is a Dusty place, Han.
Not everyone uses Genuine Air filters, rather Leepon, Guard etc. Good quality OEM standard Air filters filters dirt to even the smallest Microns, something that local filters suck at. That dirt is the mixed with the Engine Oil. Engine Oil is meant to lubricate and clean the engine.
Liqui Moly& Zic Representative told me that LM can be used for 15,000km and ZIC XQ for 25,000 KM. Too good to be true? Noap. I'll still change at 5000km. Why? I care for my engine:) Han, abroad, you can change Engine Oil later, Air filters are usually cleaned at 25,000km there, over here, every 2-3 days, a big cloud of dust comes out..... Got my point?