In the UK at least, a great many beers are marketed with a regular version and a fancier (more expensive) 'export' version. For example: Carlsberg and Carlsberg 'Export'. Is there any reason why the imported beer might be reasonably different (such as the legality of certain brewing methods outside of the UK) or is this just marketing fluff?
It doesn't actually mean anything; or at least, it almost never means the same thing twice, and doesn't refer to any specific common style or process. It's about as meaningful as the fact that several dozen breweries have a beer they label as "Select".
For example, in the case of Molson Export, the story goes that it was deemed so high quality that it was "good enough to send overseas" - and, implicitly, better than competing imported brands.
One common usage is for a line with slightly higher ABV (it keeps better in shipment!) or tailored to suit the ABC laws of other jurisdictions to which it might be shipped. But there isn't any single meaning that's widely understood.
When I visited Stella Artois brewery in Leuven (Belgium), they told us that they distributed the same beer in two kind of bottles. In brown reusable simply labeled bottles for distribution inside Belgium (note that it is a regular beer, the most drunk in Belgium), and in green more fancier labeled bottles with "imported" insciption on it for distribution around the world.
In belgium Stella Artois is a normal cheap beer, but where I live, in Spain, it is sold as imported special beer and costs more than double. However, the liquid inside the bottles is the same. So it is just marketing strategy.
The guy who showed us the brewery was clear. While people outside belgium are kind to pay more for a fancier bottle, they would distribute more expensive fancier bottles.
While I was in Germany, you had pretty much two common choices of beer available from the local brewery: Pils and Export. They were quite different, with Pils being lighter in color and taste and Export being darker and a little heavier flavor. They were in the same colored glass bottle with different labels. They are obviously two different beers. The name had nothing to do with whether it went out of the country or not. Now, maybe back when it was first developed way back when, it was exported to another people somewhere, I don't know. My beer knowledge is not that impressive, so I have relayed what I experienced.