This is, of course, a matter of opinion. My personal opinion is that it is unreasonable to expect this. The reason I say this is that western companies must be able to compete with other companies in developing countries.
If western companies do adhere to high ethical standards, they will not do such things as bribing local officials. This would be admirable, but it also seems that it would be suicidal. In countries where bribery and corruption are endemic and engrained in the system, it would be very difficult indeed for a western firm to succeed without engaging in bribery itself. It would be unable to get things like permits in any sort of a timely fashion. It would waste huge amounts of time and money while it had to wade through a local bureaucracy that was inclined to throw up more and more obstacles because of its unwillingness to pay bribes.
Therefore, so long as the developing country has a deep-seated culture of corruption, it would be very difficult indeed for western firms to adhere to the kinds of ethical codes that they live by in their home countries.