Browsers allow SSL connections to continue if CRL or OCSP checks fail with a network error because such checks can fail for a variety of reasons -- for example the CA servers are down or there's network congestion en route to them. This is known as a soft fail approach.
The problem is that man-in-the-middle attackers can also block CRL and OCSP checks, rendering the mechanism useless. Because of this, browser vendors have to manually blacklist known rogue certificates and then push the blacklist updates to the browsers.
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