On the DDI issue, one thing jumped out at me the second I tried it. It was very good for those who were already willing to invest and participate in 4E games and who are looking for 4E resources. It fails miserably as a marketing tool for newer players since the only way to know anything about it or the content on it was to actually go to WOTC's website, something not likely to happen without some kind of books and/or additional advertising to get the word out and visible to the general public. When it comes to marketing, books can to some degree market themselves, provided you can get them in a place where a lot of people will see them. This is why art is so important to rpg books; not only does it illustrate certain points within the book, but it doubles as advertising for the casual browser, giving you additional benefit for the cost of the art. It's no accident that Paizo still manages to sell books despite most of the printed content being available online; the artwork and the layout sell the books just as much as the words themselves. A pure web based presence would be near impossible to sustain at the same cost as a book based presence simply because it's so much harder to get enough people to actually come to and read your site long enough to secure a subscription. Also, you have to keep paying for servers and bandwidth or your customers lose access to everything; books, once the initial price is paid can keep generating attention for as long as people feel like looking at them for no additional cost.
Paizo's mixed approach is by far a more sound one than the DDI approach taken by WOTC. It feeds on the strengths of both mediums simultaneously, allowing each to strengthen the other, and the company's bottom line in the process, and relies as much on subscriptions as DDI does. DDI ended up cannabalizing book sales, negating whatever positives it may have provided; it didn't end up costing them money, I'm sure, and it probably did help support Next's development to some degree, but I seriously doubt that it reaped the benefits they were expecting, and it certainly didn't entirely make up for the lack of non-DDI products during the development period. In the end, subscriptions may well be the future, but the Paizo model is a lot more likely to be copied than the DDI model since it manages to embrace both the electronic medium and the traditional printed medium, which contrary to popular belief on the internet, is not going to go away anytime soon.
The OGL issue is actually very similar in the primary effect of cutting off cheap networking and advertising. The 4E license did a very good job of protecting WOTC's assets, but cut off a lot, and I do mean a lot, of comparatively cheap advertising that gave the 3rd edition, and d20 in general, such a wide word of mouth network. The OGL had holes, to be certain, and required a different type of business strategy than what WOTC was prepared for, but Paizo has shown that the holes can be filled in for the most part and that it's strengths can be emphasized so that its weaknesses have considerably less impact. WOTC's best bet for Next is to try some middle ground between the two extremes like Paizo has so that 3PPs feel like its beneficial for them to support Next just as much as they do PF.
In the end, the differences in the approaches and the net results that each company has gotten shows that long term support is indeed crucial, but, like others have stated, the nature of that support is critical. Paizo set up an environment that may have been a bit more expensive at first, but at this point is comparatively cheap to sustain, with 3PPs and a strong word of mouth network providing cheap and willing support and advertising for the many PF related product lines. WOTC chose a path that probably cost less upfront, but because they basically tried to do everything with very little to no outside support, sustaining 4E probably proved more costly than anticipated, and sustaining Next will have the same problem if they insist on going the same route. WOTC seems to rely on brand inertia carrying on forever and an ever flowing supply of rule splat books, which hasn't worked since late 3.5. Paizo relies just as much on new content, but the fact that it tends to be adventures and filling out their world rather than only new rules all the time greatly increases the value of the support given. Novels are actually a key player here in that WOTC has let this aspect of long term support wane, still relying on characters created during TSR's ownership of the brand, while Paizo seems to be doing a better job of keeping a good balance of sustaining older authors/characters and putting out new material at the same time.