When running a server on amazon aws, is there any point to placing a sql server transaction log on a separate volume from the database? Of course if I had control of the physical environment I'd place the tlog on a separate spindle or raid array. But in AWS-EC2, the windows volumes will be mapped to any number of physical drives in some unknown configuration so I'm thinking no, there's no point in it.
Well, if the db and logs are on the same EBS volume, you know they'll be competing for spindle time. At least if they're on separate EBS volumes, even if you don't know with certainty that they're on different spindles, at least there's a chance that they're on different hardware.
In addition to performance, there are several other benefits to separating them out.
I recommend you read up SQL Server in EC2, there is also a video available Configuring SQL Server in Amazon EC2: Training Video.