I'm not sure I understand. It almost sounds like the example is using change management to avoid contractual consequences, which is not the intent.
The job of the project manager is to estimate and communicate project completion date to the sponsor and relevant stakeholders. In your example, an issue caused the delivery date of a key component to slip.
Change management will help all the stakeholders to understand the impact of this slippage on their tasks. It will help to replan the project and revise the estimated completion timeline and costs.
vendor can use the change management process to increase the scope and shift the delivery date to a later date?
This seems to imply that the vendor is using change management against the rest of the project team. It might imply that the vendor is using change management as a tactic in contract management, which is quite contrary to the intent.
I'm not sure where in the example the scope has changed - the slipped delivery date for the vendor's task affects the schedule, but there is nothing in the example that would affect the scope of the project.
The precise terms of the contract with the vendor will determine which party needs to accept the consequences. Contracts are written to price risk to one of the parties; in this case, the risk (Given that software development requires some research, if the development estimate is flawed, then delivery will be delayed.) transformed into an issue. The terms of the contract will determine whether the vendor or the purchaser has to bear the consequences of that issue.