
It is common for essay-writing in British universities to be a more iterative process.
The original academic paper submission will be ripped to shreds by the student's "tutor" and will be gotten into shape through several revisions.
So companies specializing in British work tend to charge with this in mind, expecting to work on several revisions with the student.
They might charge twice the price -- and earn every penny.
The US and the UK are both based on common-law, rule of law (as opposed to rule by law) systems.
In fact, the US system is basically an extension of English common law.
Citation styles, references, and precedent may differ, but the basic framework is similar enough... plus, as pheelyks notes, the world is much smaller now, when it comes to accessing the necessary info.