Isn't that number based off the top 20 titles?

Hmm ok lets say you are publisher of dvd and bluray movies.
Do you prefer to sell 9000000 of items at 5$ each and 1000000 at 15$
or 11000000 at 5$ ?

It's not about what you'd rather sell.  From my example above, a seller may rather sell 1 movie at a billion dollars for 10% of the market rather than 100 milllion movies for $10 to get 10% of the market.  But many people would be confused if you said that the one sale was a 10% market share.

When people say "market share" they don't think revenue, they think of success based on numbers sold.  And as everyone knows, BDs are much more expensive than DVDs.

Still, it's hard to know how BD is doing in the market because all of the press releases we get extolling BD performance basically say, "BD is doing better this year than last year.  Look at how much it's doing better!"

i just cant believe Sony actually thought Blu-Ray was going to have 50% market share over dvd by the end of 08....So reality wise they have a market share of around 4%. Where on earth did they think they would be getting the extra 46% from?

Well, it would have been market share measured by revenue or possibly top-20.  So they're at 8%-10% in terms of revenue.

Sony knew it would never reach that kind of market share, but perhaps they knew of some number wrangling they could do which would give them very high market share numbers.  For example, if they had some big releases and more BD players on the market (they expected to sell more PS3s) and if there were some timed-exclusive BD releases, it could have been the case that top-5 or top-10 BDs had very high market share for a week.

The thing is, I know very few people with any kind of BD player.  But everyone I know has a DVD player.  So saying that BD is around 10% seems so misleading to me.

Of course, they're not including download market share.

There's a number of spin techniques I've seen used on Blu-Ray-related statistics... By using those, there's often the idea that Blu-Ray has 10-20% marketshare, when in reality it's probably less than 5%. Definitely misleading, but that's what PR spin does.

Blu-Ray takes up about 15-20% of the combined DVD/BD shelf space at major retailers in the US these days.

That says a lot more about its future potential than merely analyzing the current sales numbers, honestly. Retailers are pushing it. It will succeed, because they want it to succeed eventually. Has little to do with Sony, etc., really.

I have seen this type of spin used in NPD reaction press as well. Microsoft used to quote their percentage share of video game revenue, as it was greater that their market share for the month. (because of great software sales)

It can be misleading, but also useful at the same time. A game that sells 1M copies for $20 each has less revenue that a game that sells 500K copies at $50. Revenue does matter to game makers.

What is the best way to measure Blu-ray's success or failure? It is difficult to compare it directly with DVD because DVD is the entrenched technology. Much like we don't include the PS2 when we discuss console sales this generation. If we are excited about comparisons, let's start to compare Blu-ray to digital distribution.

Well it's tough to compare DVD to Blu Ray directly. If you're going by units sold your not adressing the significant cost differential between the two formats. If you go by revenue it doesn't show how much of an uphill clime BR has to penetrating homes that overwhelmingly use DVD.

I think you go by units but there's no perfect way to measure it. There won't be one significant point where we can definatively say blue ray has captured 50% of the market. Sony and BR forces will use the numbers that skew their way, while their detractors will use numbers that skew the other way.