Folk, your first question can basically summed up as, why are different doctors using different Lyme tests? The answer is because there is no standard test in the absence of a gold standard (culture) for testing. However, it is likely and logical that Lyme is underdiagnosed rather than overdiagnosed using the two-tier test.
Re: Rituximab, you´ll notice that KDM mentions that it ´ME/Chronic Lyme´is no longer a purely infectious disease, i.e. there is likely to be an auto-immune component too. There was a thread posted in the Lyme forum yesterday about the potential benefits of Dexamethasone in Lyme, another drug (like Rituximab) that is used in Rheumatoid Arthritis, an auto-immune condition.
The first one isn't actually an answer... Since there ain't no reliable tests, there ain't no reliable results. Even though you find it logical that with the two-tier test Lyme ends up underdiagnosed, it is also logical that unreliable tests aren't the way of correcting it. Creating false positive results won't make up for the false negatives of the two-tier test.
Still most Lyme specialists claim that Lyme is a clinic diagnostic, which in my opinion just means: If you go first to a ME specialist he'll say you have ME, if you go first to a Lyme specialist he'll say you have Lyme, and if you go first to any other doctor he'll say it's in your head.