Windows Phone is a unique operating system, both in terms of function and the community. One undervalued aspect not found on other competing platforms it 'trial mode' for apps and games. Microsoft has even made the process relatively easy for developers in apps (although games can be trickier). Intrinsically, trial modes are commonplace on Windows Phone, and it befits developers to implement the feature if they want good ratings.
Recently at Windows Phone Central when we covered the new game Lost Echo from KickBack studio (www.kickback-studios.com), our audience rebuked the $2.99 game due to the lack of a trial. The highly regarded game had come from iOS before it made the jump from to Windows Phone.