There may be differing costs for payment processing too, and if they have any sort of tech support and documentation there will be larger internationalisation costs in Europe too.
These things are unlikely to explain all the difference (probably not even close to half of it) but we need to consider these thing to make sure we are being fair when shouting "rip off!".
Also, regarding i18n for Europe: most of the time, it is localized only for FIGS (France, Italy, Germany, Spain). Other 20 or so (for EU, not Europe) countries get shown a finger. So why should they pay for that?
On internationalisation: fair point on those that don't get the effort, though some effort being made is better than none.
Do you have a source for that? According to this [1] Europe has by far the cheapest bandwidth in the world
[1] http://blog.cloudflare.com/the-relative-cost-of-bandwidth-around-the-world
In Dropbox example both include VAT. You can see this tendency clearly in digital games. When I worked with games pricing for MacOS, I asked why such a huge difference? Boss replied: "It is the easiest to force Europeans into premium costs".
There is even a chrome extension which shows how much a game costs in different countries on Steam website:
Buy Sid Meier's Civilization V
US: $29.99 (18.04 GBP)
RU: 249 pуб. (4.01 GBP) (78% )
CIS: $14.99 USD (9.02 GBP) (50% )
BR: R$ 44,99 (12.11 GBP) (33% )
UK: £19.99 (11% )
EU: 29,99€ (23.7 GBP) (31% )
AU: $69.99 USD (42.11 GBP) (133% )
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Also not long time ago there was an article about Spotify pricing [1]. It simply is a many years ongoing Europe rip-off.
[1] - http://mts.io/projects/spotify-pricing/