Great Western Coffee Shop

I understood that if trains were cancelled due to the effects of bad weather, the Train Operating companies are not obliged to provide replacement transport [by road in this case].  And yet here's an example where such replacement does seem to be being provided.  Are Arriva Trains providing the bus for contractual reasons, or over and above their contract as a good piece of customer service?

Possibly to appease the Welsh Assembly.

They're not obliged to but they will whenever possible, eg if flooding blocks Oxford-Didcot in the next few days. However, if road conditions are considered too dangerous by the bus and coach operators, as was the case in many places in the past couple of weeks due to the snow, they can't provide a replacement.

Had the Cotswold Line got blocked by snow, they simply couldn't have done anything to cover most places the trains serve. And I don't just mean down the side roads. Stagecoach suspended the S3 between Oxford and Chipping Norton along the A44 several times due to snow and ice and didn't run a single S3 into Charlbury for a week.

I should imagine in this case there are no trains running at all betweem Carmarthen and Swansea so road replacement transport is on operation.

Flooding has been pretty bad in the area around Llanelli so this is probably the reason why but it's not impassable for road transport as obviously they can around problem areas. It may be seen as being provided by ATW as they recently created a road transport unit for the provision of rail replacement or providing busses for major events (the recently gained Ryder cup contract being an example)