They are all called i7 processors
Most of the time when people are talking about i7 processors, they refer to those really powerful, quad core variants, those that have a "MQ" (Haswell) or "QM" (Ivy Bridge/ Sandy Bridge) suffixes in the code name

There are some dual-core i7 processors as well, which are essentially higher-clocked i5 processors.
Those come with suffices "U" (Haswell) or "M" (Ivy Bridge) etc.
These processors are probably marketing gimmicks to attract less informed users?

* Sorry if I left out something haha XD

huh? 
There got to be some misunderstanding here
Just to make this clear.
An i7 that has a U suffix is only duo core.
An i7 that has MQ (or QM) suffix is quad core.
i7-4700MQ and i7-4702MQ both are quad core.
i7-4700MQ run slightly faster (2.4GHz turbo to 3.4GHz) compared to i704702MQ (2.2GHz turbo to 3.2GHz), but draw more power (47W TDP vs 37W TDP). Pro - better peak performance (if temp is under control and no throttling). Con - shorter battery running time.

Whether the laptop is durable or not is depended on your TLC, and lots of luck
Lots of multi-task, get more RAM. 4G stick ~ RM100, 8G stick ~ RM200.
Smooth - get SSD. 128G ~ RM300, 256G ~ RM600.
Unless you do heavy lifting in Photoshop, you don't need powerful spec.

15"
Asus
N550JV-CN077H, i7-4702MQ + Nvidia GT750M + (1920x1080; IPS matte) + Bluray@RM3699[2.7kg], 4GB, 1TB, W8, backlit keyboard

Dell
Inspiron 15R, i7-3537U + AMD HD8730M + (1920x1980; anti-glare)@RM3299[2.32kg], 8GB, 1TB(5400rpm), W8SL

Lenovo
Y510p, i7-4700MQ + Nvidia GT750M(GDDR5) + (1920x1080)@RM3099[2.7kg], 8GB, 1TB, W8, red backlit, swappable ODD, 120w psu, 2 yrs

MSI
GE60K, i5-3230M + Nvidia GTX660M + (1920x1080; anti-glare)@RM2899, 4GB, 750GB(7200rpm), W8, 2 years warranty
GE60-2OC, i7-4700MQ + Nvidia GT750M(GDDR5) + (1920x1080; anti-glare)@RM3099,8GB, 750GB(7200rpm), W8, steel series KB
GE60-ONC, i5-3230M + Nvidia GTX675M + (1920x1080; anti-glare)@RM3299, 4GB, 750GB(7200rpm), W8

www.illegear.com
Illegear RE-15, i7-4700MQ + Nvidia GTX765M + (1920x1080;matte)@RM3599[Onkyo], 4GB, 500GB(5400rpm), FreeDOS [CPU Options: i7-4700MQ - i7-4900MQ][/color]

13"
Asus
UX31A-R4005H, i5-3317U + Intel HD4000 + 128GB SSD + (1920 x 1080)@RM3599[1.3kg], 4GB, W8

Dell
XPS13, i5-3337U + Intel HD4000 + 256GB SSD + (1920x1080)@RM3999[1.36kg], 8GB, W8, backlit

Samsung
Series 7 Ultra, i5-3337U + Intel HD4000 + 128GB SSD + (1920x1080; anti-glare)@RM2999[JBL][1.46kg], 4GB, W8

Prices are RSP, negotiable.

Not really, iirc its pretty expensive, especially when the warranty support is bad 

Not so sure, since a lot of people complain ASUS local warranty service are Legendary bad, so I just skipped buy ASUS brand product go for others.