Regulatory lock-in is certainly one method of guaranteeing rent. I'd argue copyrights and patents are as well. Microsoft and Google get accused of rent seeking because of their near monopolies, but I don't think most of their income is particularly based on regulation. You find other forms of lock-in can come from network effects in social media (Facebook), or B2B lock-in due to outsourcing of basic business operations (IBM, Oracle, Salesforce).
I think the accusations can be divided into several categories:
- actual rent-seeking (as you say, not really true for companies such as Microsoft and Google, except where you see e.g. government documents needing to be submitted in Word. But that's very likely incompetence on behalf of the bureaucracy rather than Microsoft)
- having a dominant market position due to having a very high quality product, or set of products that work together well
- a random grudge phrased as rent-seeking, because the Twitter user in question doesn't know what rent-seeking is, but has seen their friends accuse companies of it
I don't know what the proportions are, but I suspect the former is minimal to nonexistent for e.g. Google.
