Even before Simple Delivery I always found that buying postage for posters in a tube did not fit ebays postage options as it generally exceeded the 61cm longest length for a medium parcel (or Cabin Luggage as ebay called it!) so whenever I had to post a tube (which I have done about 30 or 40 times in the past) I bought the postage directly from the Royal Mail website as the had a special category for posters whereby they were classed as a medium parcel even though they were longer than 61cm.
So, I guess postal tubes not being covered by Simple Delivery is no great shock as ebay didn't realise that their model didn't cover it previously either!
Incidentally, if sending by Royal Mail the maximum length of tube they will accept is 90cm and the length plus twice the diameter must not exceed 104cm.
And, a tube of that maximum size is still classed as a Medium Parcel by Royal Mail.
Hope that information helps a little, even if it doesn't answer the simple Delivery question!
