That's down to numerous reasons though - poorly optomised software, no support for the extra cores, overclocking (still possible on a phone), etc. Having dual core in an age whereby we are getting more and more cores per proc than ever before seems a little backwards. It's not neccessarily required but it's limiting. it's quite obvious, if optomised, that a like for like dual core vs quad core (i.e. same Mhz) the quad core will outperform it.
Yes, four of the same core will outperform two, obviously, but two better cores may beat four. Look at the Nvidia Tegra 3 vs the Snapdragon S4. I know which I'd rather have, given the choice.
Having more cores available future proofs the phone somewhat. I can see what Apple have done and some people will praise the cleverness while other people will get annoyed. Locking the phone so that you can't easily change the battery, add memory, etc. is great from there point of view because if the battery fails then it's a new phone, if you want more memory then it's a new phone.
Obviously the more powerful the hardware the better, but the amount of cores isn't necessarily the most important factor.
You have to remember that Apple are now behind the S3 in specifications and need to catch it up - I wouldn't want to buy an iPhone that's lower spec than a phone that, when the IP5 is eventually released, could have been in the market place for 6-12 months.
I doubt it would be a lower spec phone, what if it has two cores but is a lot faster and benchmarks faster? Will you still assume it's worse just because it's not quad-core?