The reason the contract is written that way is because all of the things that you want cost money.
- Exchange rate hedge? Costs money. If you want it you could either buy the currency ahead of time or buy your own hedge. If the manufacturer does it then you will have to pay for it.
- 2 year warranty? Costs money
- Engine warranty? If the engine goes pop would you rather send the engine back to the manufacturer in Eastern Europe for them to send on to Rotax, or deal direct with the Rotax agent in the UK? (That said, my personal experience with Rotax is that their goodwill on engines which go bad even days out of warranty is zero, and they can get away with it because they are a monopoly supplier)
The problem for the customer is that you are paying Mercedes money but don't get Mercedes-level service. This is because there are very few companies making any significant amount of money out of selling light aircraft, and that is reflected all the way down the supply chain.
I'm not saying that any of these things are "right" or satisfactory for the customer, but that is the way it is. If you find the terms unacceptable your only options are either to renegotiate them or go elswhere.
Would you rather have your contract direct with the manufacturer, or with a UK agent who may have no assets and could spend all your money on running their business rather than passing it on to the factory?