By not being native fpGUI faults the user while trying to apply a cross-platform corporate symmetry.
Such statements always makes me laugh.

Lets be realist, if the person that pays me to develop
their app wants pink polka dots on their user interface, then they WILL get pink polka dots. Who are you, me, some OS or some open source project to dictate to the
paying customer what he or she may or may not get.
LCL and fpGUI cater for different needs - simple as that.
On a side note:Web Apps - no native look (yet millions of Internet users have no problem with that) , Qt (most popular gui toolkit around) - not a native toolkit - all custom drawn, Microsoft Office (most popular office suite) - lots of custom components, Media Players - lots and lots of custom components, Mobile Devices - lots of non-native components and apps.
People and companies want their products to stand out above the rest, that is why Microsoft makes Office, Visual Studio, IE etc look different to the rest of Windows. Same goes for Mac OS X. It's all about branding! LCL stifles this, and that is why I was asked to develop fpGUI (at least that was one of many reasons).
Take a look at a fpGUI interface on a larger resolution with a larger DPI.
That depends on the app. Our commercial apps scale perfectly with DPI changes, but we added that functionality ourselves - it doesn't come as standard with fpGUI yet. Same applies to LCL. Lazarus IDE (compiled for GTK2), among many other apps, don't scale well on my system either.
Bottom line... if fpGUI doesn't suite your needs, simply don't use it.