I would respectfully disagree with the number crunching comment. By the early 5th century the Romans were huge number crunchers. Armies of accountants had to be employed to estimate the needs of the empire. Keep in mind soldiers and administrators had to be paid in currency (gold and copper mainly), rations and equipment had to be distributed (payments in kind), recruits had to be raised and equipped, and public lands and buildings had to be maintained. Each administrator was responsible for estimating his needs then sent his budget to the central authorities who somehow had to figure out how to shift resources around to even things out. This done on a yearly basis. To make matters worse a lot of the figures I've seen often were not rounded to the nearest whole number (they were using odd fractions like 5/8ths). Most taxes were based on land so surveyors had to go out often to assess landowner resources, grade the quality of the land then calculate the taxes due. Again an incredible task considering the number system they used and the lack of paper to record thier figures. The fact that the empire lasted so long is a testament to Rome's greatest attribute in my opinion, superior organization.
The point I think you are trying to make is that Rome's lack of technological breakthroughs (like we see today) contributed to its downfall. That's a bit unfair. One could ask why didn't the industrial revolution happen in Arabia, China or MesoAmerica just as easily. All countries, like men, must die.
Metforce