We agree that there are many similarities between RSVP and normal reading. There are, however, also reliable influences on reading fixations from upcoming words that, by definition, are absent in RSVP. Obviously, these so-called preview benefits and parafoveal-on-foveal effects are absent in RSVP reading (see Kliegl, Nuthmann, & Engbert, 2006; Rayner, 1998, for reviews). Moreover, even in RSVP it is not clear that word processing is strictly serial. Possibly, an earlier word is still being processed while the next word is presented. Indeed, given the high-speed experimenter-paced presentation, this seems a very plausible scenario. It was unclear to us how the present experiment could distinguish between serial and parallel processing of words, given that the performance also depended on the retrieval of information after a string of six words. Retrieval itself may additionally bias the processing towards seriality.

References:
Kliegl, R., Nuthmann, A., & Engbert, R. (2006). Tracking the mind during reading: The influence of past, present, and future words on fixation durations. Journal of Experimental Psychology: General, 135, 12–35.
Rayner, K. (1998). Eye movements in reading and information processing: 20 years of research. Psychological Bulletin, 124, 372–422.