[ntalbott]

The data is absolutely transferrable today - we've had multiple customers leverage that transferability to switch (or augment) their gateway with just a configuration change.

Of course, it's not just about data portability; API consistency is a big deal as well. If PayPal (for instance) decides to lock down your account and not let you transact any longer, you don't just have to worry about getting your data out, you are also looking at another whole implementation cycle around a new API. Even if it's just a day of work (and usually it takes longer), that's a day you could've spent on your product instead of mucking around with gateway API's.

There are of course libraries that help make gateway API's more consistent, but as a committer on what is in my opinion one of the best - ActiveMerchant - they only get you so far. For instance, Core gives you transparent redirect on top of any gateway we support. That means lowered PCI compliance requirements and a great experience for your customers, and there isn't a library out there that can do that for you.