The 50 transaction limit is to conserve system resources. Allowing people to download potentially 10s of thousands of records at a time will have adverse effects on the overall performance of the application for all users.
Just interested to know why you need to download all the ledger records?
Also you can actually export a detailed list of all nominal ledger records, take a look here. Furthermore you can request a backup of your account, this will also contain a full CSV list of ledger entries, clients, suppliers, invoices, bank transactions etc.