Google Maps can't calculate a route that crosses Equator - Colombia borders, and this analysis from a Wikipedia user shows the regions it considers contiguous. It is possible to compute a route in Yahoo! Maps from Punta Arenas to Maracaibo, but not to Alaska.
Why does this services have such limitations? Is there a similar analysis of contiguous regions for other web routing services?
The closest similar "analysis" I know of for Bing Maps is the table given at http://msdn.microsoft.com/en-us/library/dd435699.aspx, which shows the routing capabilities provided for each country (Basic/Full).
Interestingly, even though both Ecuador and Colombia are listed as having only "Basic" routing functionality, Bing Maps does correctly find the route between Tulcan and Ipiales shown in your first example: http://www.bing.com/maps/#Y3A9MC44MjE2NDA5OTgxMjgxNn4tNzcuNjg2OTIzOTgwNzEyODkmbHZsPTEzJnN0eT1yJnJ0cD1wb3MuMC44MjE1MjBfLTc3LjczMjE3MF9UdWxjJUMzJUExbiUyQyUyMEVjdWFkb3JfX19lX35wb3MuMC44MjE3NjJfLTc3LjY0MTY3OF9JcGlhbGVzJTJDJTIwQ29sb21iaWFfX19lXyZtb2RlPUQmcnRvcD0wfjB+MH4=
I guess the reason why routing capability must be compartmentalised into discrete countries is because the data required is gathered from national agencies (e.g. government datasets) and managed/updated on a per-country basis - but this obviously creates an interesting problem for routing across borders, as in your examples.
I have to be honest and say that I've never really considered the issue before, so I'd like to thank you for raising the question!
Update: Note that, according to the spreadsheet linked from https://developers.google.com/maps/faq#whatcountries, Google Maps doesn't support directions within either Ecuador or Colombia either - let alone a route that crosses between them!
