In my, albeit limited, experience in the workplace it appears as though the culture of referring to one's superiors by their surname is almost entirely absent. Is this merely a reflection of my company's culture (I work for a large multi-national tech conglomerate) or is it indicative of a trend in industry at large?
I would say this heavily depends on the situation but ill list a few common ones that I have come across,
If you are emailing someone outside of your company in a professional capacity whom you have not yet met, a proper Mr./Mrs./Ms. is often used.
If you are emailing someone outside your company whom you have met and become aquatinted with you can go either way.
Internally the formality is all but gone in my experience. For that matter I have noticed some people not even address the email to the individual if sending it to only one person.
The major decision situation is for marketing/sales related email. There is plenty of info out there on addressing sales/marketing material to strangers that heavily changes the tone of the email.
On a somewhat controversial note there are people who belive that you should not assume gender (which these prefixes tend to do) and you should either drop the prefix or only use it if you know which one they prefer.
Reflecting on @Dave's comment this seems to be largely cultural. I'm in Australia and over here it would be seen as quite unusual for me to e-mail somebody new by salutation/title. Typically (here at least) I would address them by name and in the first sentence be sure to introduce myself and provide a quick summary of the context of my reaching out to them. If somebody referred me, I'd namedrop that person early to allow for more context.
Given that you work for a multi-national organisation chances are whatever approach you take is fine, just follow the same vibe as what your colleagues close by are doing. If I were to receive an e-mail from the Philippines and it was worded a bit differently, I'd chalk it up to cultural differences. I don't see why your international colleagues wouldn't do the same.