There's "some" truth to that advice, but I don't think the replacement schedule should be that strict. The bulb replacement schedule should be based on operating hours at the very least, not "just toss'em after 8 months". There are other variables to consider, that don't appear to be weighed with that logic. I used to replace mine when it became obvious that they weren't putting out as much light. That used to occur at around the 20 month mark for me. "Your results may vary".
I know T5HO bulbs will last around 2 years, with no real problems. PC bulbs, like the 55 watt one used by AH Supply, don't last as long before their intensity drops significantly. T8 bulbs seem to lose intensity in a year or so. Obviously that will all depend on how many hours a day you keep them on.