They "Cheat" the number of speakers in the ML system. They count a 2-way speaker as 2 speakers. Gotta love marketing
Also, it seems the people are forgetting that you're dealing with an amplified system in the Alpine. Your speakers are not being powered with 5-10 watts RMS by a head unit...its a standalone amp pushing them.
Sorry, not to offend anyone, but those who say you will not notice any improvement in sound just by changing speakers are simply wrong. Will the difference blow your face off? Nope, but there WILL be an improvement, and one you'll notice.
IF you upgrade to a more efficient speaker, you WILL notice a difference. I doubt the factory alpine speakers are over 85db sensitivity. Find a good speaker with 90+db's sensitivity, and your sound will improve.
The Focal K2's that were just added have a sensitivity rating of 93db's and run off of 6-80 watts RMS.
One of the most popular home speakers out there, Klipsch, has made their name on efficiency. By using a horn and proper cabinet architecture, their infamous K-Horns have an efficiency of 104db and can hit 115 decibels off of one single watt.
Simply said, a speaker with higher sensitivity will use whatever power they're getting better..and you'll hear it.