Something having it's price lowered is generally a bad sign. A bundle deal however is generally not.
If you lower a price of a product shortly after its released, you either:
A) Overestimated the value of your product relative to the competition.
B) Overestimated demand for your product.
C) Decided you could get more sales at that price level to make more of a net profit than keeping the previous price.
D) Some combination of A, B, and C.
My opinion is that HP committed 'A' and is responding with 'C'. I don't think this is necessarily a bad thing for webOS overall, $399 should be the price of a webOS tablet. HP is a value brand in the eyes of most consumers. Tablets are typically a consumer product. Sure HP makes amazing machinery (Indigo Presses, servers, etc), but the simple fact is that a consumer things of cheap laptops/printers at Best Buy when the see the name HP.
$399 for a 16GB tablets plus some discounts on top from people like Amazon is enough space between the ipad to sway someone to give it a try. More importantly, as webOS 3 improves through updates the in store impressions will get better. Hopefully the Opal tablet is a bit sleeker than the Touchpad and gives a better physical first impression and comes in at an even lower price point. I think many companies would have a hard time fighting a $300 dollar webOS tablet.
In any event, HP needs to lose money to sell these things if that's what it takes, because critical mass is needed to get the ball rolling on third party development. Hopefully if HP can get the tablet count near a few million all of them running webOS 3, they can make a strong pitch to indie developers and big name dev's alike.