Yes, very few people who run and/or complete a marathon are running, or even peak at, 70mpw. A lot of the faster people are, but "faster" is a relative term. A guy/gal running a 2:55 is "faster" than me, but that's not really very fast in the big scheme of things. If you want some decent free plans for different levels of runners to look over and possibly put into practice, take a look at Hal Higdon's web site (Google Hal Higdon). If you feel like Higdon's site is too cheesy because he's a free resource for thousands (at least) of everyday runners, which most of the wannabe's on this site ARE by the way, go buy a book by Daniels, Pfitzinger, Hansens, etc. They generally cost less than $15 and provide a great deal of useful information, some even for multiple distances such as the Daniels book that covers distances from cross country to the marathon and most distances in between.
BTW, the answer to your original question is No. When you do a "cut back" week, most coaches generally suggest you cut your weekly mileage by about 25-33% and also cut your LR by a few miles as well. For instance, if your mileage this week was 40 and your LR was 15, for your cut-back week you'd cut the mileage to around 26-30 and the LR would be 10-12.
Good luck, you've got plenty of time to train for an enjoyable marathon as long as you have realistic expectations for race day.