All it really says is that in the early months, there are no solo engagements planned. I think that's fair enough - I think anyone would want to get some more experience in such a high profile role before going solo. The Canada trip in July will be an important step towards that.
Also, she'll be inundated with offers for things like charitable involvement, and I expect it will take some time to work out how much she can take on, when and for whom. I think it took a while before Diana took on an independent role too - the only difference really beingbthat Charles had a full load of public engagements at the time of his marriage, whereas William has a full-time military role yet still manages a representational one on top of that.
And I think portofino's point about the Queen taking the opportunity early in her married life to have a little while living as privately as possible is well made, and I don't begrudge the Cambridges a similar chance.
And I'd guess that the thank-you letters would be a nigh on full time job for a while!