I honestly agree with both sides - in the end, less plastic bags is a good thing but they are also saving money ... those are the best plans for companies and generally what motivate them: if it makes us look good by being "green" but also save money, win-win
For example, my company recently installed the largest solar panel field in the county ... now, it makes them look great and fits in with their "sustainability" mission - but they were very obvious that the system will has a life span of 17 years and will pay for itself after 10 - so it makes financial sense as well
To me the biggest giveaway of the real intention is:
A) there already exist environmentally friendly alternatives to plastic bags, including biodegradable "plastics", which biodehrade quite quickly and safely but do cost a little more.
B) This is clearly going to save them money and there is no announcement about passing on savings or any such thing or doing something environmental with the savings.
C) they are removing an important convenience (bags) but offering an alternative (relatively expensive bags that are probably as bad or worse, if even more non biodegradable materials are used in them compared to regular plastic bags) and passing the cost onto the customer and, lets face it, making a profit off those bags too i imagine.
Their interest is in making money and cutting costs, not going green.