That 100,000 miles on the GLI??!! Of course there's some deposits built up. Especially since it's a notorious VW problem that they hate low speed running and load up super bad when you do. And the deposit level on that 50,000 mile 3 doesn't look that bad, nowhere near enough to freak out about.
Given the general level of maintenance American-driven automobiles receive (namely, nearly none until they break) it's no surprise to find deposits, most people don't change their oil nearly often enough and that's a major cause of deposits.
There are far to many potential causes of deposits to blanket say we all need to Seafoam our 2 year old cars. It's all about maintenance and treatment. If you've been using your 3 as a taxi or police vehicle or as a delivery vehicle for UPS and, failing to maintain it, maybe you should get at this but, given good, normal treatment/maintenance, it's probably premature for most of us.
I am old enough to recall when decarbonising an engine was a normal service. This meant a complete teardown and hot-tank at specified intervals, if you can believe that.
This is what Seafoam and other products were designed for, not for modern, EFI and computer equipped cars. This doesn't mean deposits don't form and affect performance but, it's ALOT further down the road than it was in those days.
but, I do have the deadly downpipe and race pipe combo that seems to be the cause of most PCV related upset. I did put it in BEFORE I saw any turbo smoke 
