Actually what speaks volumes is that they have not communicated...

Actually what speaks volumes is that they have not communicated this correctly or you dont understand.

If an employee is paid monthly at the mid month - That is only they payment cycle. You are paid for the month to that mid month date. So the day before they pay you you have funded the company for 1 day less than the month.

If you are paid fortnightly in fact you can only have 13 days that they owe you for.

Your argument is incorrect. All employees only get paid in arrears - The arrears is either monthly or fortnightly.

Monthly funds the company more than fortnightly.

This is not rocket science - bag the company if they are wrong but when they are doing something that benefits the employee and then they get bagged - that is really bad.