I think there's a lot of confusion about the light levels required for a projector. When people say you can't use them in daylight that doesn't necessarily mean you need an almost pitch dark room either. Most living rooms are considerably darker than daylight (ie outdoors) and if you draw the curtains the room is probably still perfectly light enough to see in but it should be quite dark enough for viewing.
A lot of business presentations on projectors are made in well lit boardrooms and it's not necessary to turn the lights out. 'Business' projectors tend to have higher lumens (and less contrast) than home cinema projectors but I would say that with around 1000 lumens you should be fine in most rooms even if you don't draw the curtains providing you don't have light streaming in through a window right onto your screen.
Obviously the darker the room the better contrast you'll get so if you're just watching the news, no worries, but wait until it's dark and draw the curtains if you're about to do a Lord of the Rings session
Gives an idea on how many lumens are needed for an adequate picture in situations where light is unavoidable. Although a lot of manufacturers over rate their lumen which is why you should always try before you buy.
True, ANSI lumens does seem to be subject to some variation in how it's measured, although it is supposed to be a fairly objective indicator.
A recent PC Pro Labs Test took on about 15 projectors and they did their own measurement of brightness, with results which varied enormously against the manufacturers' claimed brightness levels.
Hitachi tend to be very conservative with their claims. Epson, too, seem to be reasonable about it. Some of the others are well in touch with the fact that most people go on price vs spec, and so take the manufacturers' own ratings very literally.
However, don't be fooled into thinking that it's all about brightness. If you're using your projector for home cinema, contrast is as important if not more so. It's no good having a super-bright image if the blacks are nearly as super-bright as the whites!!
Be realistic about the conditions in your room. It may be daylight outside, but if there's only one medium size window you can get away with about 1200 lumens and still watch films in the day. Whatever the projector, it's always better to cut out the ambient light. The projector can't make the screen darker to show blacks - it can only make you perceive black because the white is so bright.