There is no general, blanket presumption of consent. Even a married woman, who has an ongoing legally-recognized sexual relationship with her busband, can prosecute for rape if she can prove force, threat of force, or explicit coercion (overriding her right to consent or refuse.) Hard to prove perhaps, rarely leading to conviction perhaps, but she still has standing to bring the charges.
You raise an interesting point. What you say may be true in most jurisdictions now, but it's a legal novelty unique to modern Western culture that bubbled up in recent decades. It's an absurdity when you think about it, because marriage is a continuous process both parties have agreed to in advance. The financial support and physical protection a husband is obligated to provide is not an individual event, but an ongoing privilege and responsibility. The same applies to the unique conjugal rights—they have traditionally been regarded as rights—that a man and wife have to each other's person. Talking about "rape" in this context is like bringing trespassing charges against you for trying to move into an apartment you've rented.
If you read the tomes from the 1960s and thereafter on the then-new idea of "marital rape," you quickly discover that, as legal theory, it was designed to undercut the privacy, unique legal privileges, and binding nature of the marriage bond. Your example is a classic case of the hard case that makes bad law. The benefits of marriage are inseparable from its irrevocable, total nature, of two people who own each other. Those intent on the destruction of marriage realized this, and designed their doctirne accordingly.