They share a lot of parts.  But remember, the big deal about these vehicles
has to do with the body and layout, not the drive train.

I have worked on older RR cars, though not any of the newer ones.

They are different vehicles for different applications.  They are not
designed to make the driver happy, they are designed to make the passenger
happy.

Yes, they'll last for 500,000 miles with original engine and transmission,
BECAUSE the maintenance schedule on them is so extended.  Hell, some of the
older RR vehicles specify chassis lube every 500 miles.   If you put that
kind of PM and attention into a Toyota it would last for 500,000 miles too.
It's expected that if you have one of these vehicles that you have a driver
and mechanic to take care of them, so they are designed to actually be
maintained, unlike most cars today.  

But what you REALLY get is a driver/passenger configuration that is intended
to make the passenger in the back seat comfortable while his driver does all
the work.  This is something that isn't very common, and any time you want
something that not everyone else wants, you pay more money because you don't
get the benefits of mass-production.
--scott

The image of the Bentley is somewhat sportier than the Rolls.
Volkswagen actually bought both names from their prior owner, although
BMW now has the right to produce Rolls Royce cars.  Are they BMW Royce
and Volksentley cars now?

Not  me.

Are they half a million bucks better quality than say a Lexus or a
Toyota?  Probably not.  But they do have really nice looking
interiors.

Beyond a prestige name you get a lot of bragging rights and the right
to enjoy the heads that will inevitably turn as you silently and
quickly motor past.   And you will  take pleasure in knowing you will
be immediately identified as either having the balance sheet  and
income statement to support such an Automotive Investment or an
American Express Card that will support a short term luxury car rental.

A friend let me drive her fathers Rolls once.   Its the only car i was
nervous to drive.  I noticed when I closed the door it seems to have
some sort of vacuum that helped close the door very easily and silently.
(Possibly the passenger compartment received a slight vacuum to pull the
door closed.)  No slamming of door needed.

When I started it, motor was so quiet with no vibration, i couldn't tell
if it was running.

When I put it in drive there was no lurch or creeping forward like on
other automatic cars.  It just stayed in place until I pushed the gas
pedal.

I felt like the seat was mounted high like i was sitting high up and
kind of looking down.   I was so nervous that I might damage or wreck
the car my foot was shaking.  But it was a once in a lifetime
opportunity for me.

I think the Rolls uses 7 quarts of oil and comes with Michelin tires.
Since they spare no expense its a feather in their cap to be the tire of
choice.